This Clause describes components that C++ programs may use to perform input/output operations.
The following subclauses describe requirements for stream parameters, and components for forward declarations of iostreams, predefined iostreams objects, base iostreams classes, stream buffering, stream formatting and manipulators, string streams, and file streams, as summarized in Table [tab:iostreams.lib.summary].
| Subclause | Header(s) | |
| [iostreams.requirements] | Requirements | |
| [iostream.forward] | Forward declarations | <iosfwd> |
| [iostream.objects] | Standard iostream objects | <iostream> |
| [iostreams.base] | Iostreams base classes | <ios> |
| [stream.buffers] | Stream buffers | <streambuf> |
| [iostream.format] | Formatting and manipulators | <istream> |
| <ostream> | ||
| <iomanip> | ||
| [string.streams] | String streams | <sstream> |
| [file.streams] | File streams | <fstream> |
| [filesystems] | File systems | <filesystem> |
| [c.files] | C library files | <cstdio> |
| <cinttypes> | ||
Figure [fig:streampos] illustrates relationships among various types described in this clause. A line from A to B indicates that A is an alias (e.g. a typedef) for B or that A is defined in terms of B.
No function described in Clause [input.output] except for ios_base::imbue and basic_filebuf::pubimbue causes any instance of basic_ios::imbue or basic_streambuf::imbue to be called. If any user function called from a function declared in Clause [input.output] or as an overriding virtual function of any class declared in Clause [input.output] calls imbue, the behavior is undefined.
The classes of Clause [input.output] with template arguments charT and traits behave as described if traits::pos_type and traits::off_type are streampos and streamoff respectively. Except as noted explicitly below, their behavior when traits::pos_type and traits::off_type are other types is implementation-defined.
In the classes of Clause [input.output], a template parameter with name charT represents a member of the set of types containing char, wchar_t, and any other implementation-defined character types that satisfy the requirements for a character on which any of the iostream components can be instantiated.
Concurrent access to a stream object ([string.streams], [file.streams]), stream buffer object ([stream.buffers]), or C Library stream ([c.files]) by multiple threads may result in a data race ([intro.multithread]) unless otherwise specified ([iostream.objects]). [ Note: Data races result in undefined behavior ([intro.multithread]). — end note ]
If one thread makes a library call a that writes a value to a stream and, as a result, another thread reads this value from the stream through a library call b such that this does not result in a data race, then a's write synchronizes with b's read.
namespace std {
template<class charT> class char_traits;
template<> class char_traits<char>;
template<> class char_traits<char16_t>;
template<> class char_traits<char32_t>;
template<> class char_traits<wchar_t>;
template<class T> class allocator;
template <class charT, class traits = char_traits<charT>>
class basic_ios;
template <class charT, class traits = char_traits<charT>>
class basic_streambuf;
template <class charT, class traits = char_traits<charT>>
class basic_istream;
template <class charT, class traits = char_traits<charT>>
class basic_ostream;
template <class charT, class traits = char_traits<charT>>
class basic_iostream;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringbuf;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_istringstream;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_ostringstream;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringstream;
template <class charT, class traits = char_traits<charT>>
class basic_filebuf;
template <class charT, class traits = char_traits<charT>>
class basic_ifstream;
template <class charT, class traits = char_traits<charT>>
class basic_ofstream;
template <class charT, class traits = char_traits<charT>>
class basic_fstream;
template <class charT, class traits = char_traits<charT>>
class istreambuf_iterator;
template <class charT, class traits = char_traits<charT>>
class ostreambuf_iterator;
using ios = basic_ios<char>;
using wios = basic_ios<wchar_t>;
using streambuf = basic_streambuf<char>;
using istream = basic_istream<char>;
using ostream = basic_ostream<char>;
using iostream = basic_iostream<char>;
using stringbuf = basic_stringbuf<char>;
using istringstream = basic_istringstream<char>;
using ostringstream = basic_ostringstream<char>;
using stringstream = basic_stringstream<char>;
using filebuf = basic_filebuf<char>;
using ifstream = basic_ifstream<char>;
using ofstream = basic_ofstream<char>;
using fstream = basic_fstream<char>;
using wstreambuf = basic_streambuf<wchar_t>;
using wistream = basic_istream<wchar_t>;
using wostream = basic_ostream<wchar_t>;
using wiostream = basic_iostream<wchar_t>;
using wstringbuf = basic_stringbuf<wchar_t>;
using wistringstream = basic_istringstream<wchar_t>;
using wostringstream = basic_ostringstream<wchar_t>;
using wstringstream = basic_stringstream<wchar_t>;
using wfilebuf = basic_filebuf<wchar_t>;
using wifstream = basic_ifstream<wchar_t>;
using wofstream = basic_ofstream<wchar_t>;
using wfstream = basic_fstream<wchar_t>;
template <class state> class fpos;
using streampos = fpos<char_traits<char>::state_type>;
using wstreampos = fpos<char_traits<wchar_t>::state_type>;
}
Default template arguments are described as appearing both in <iosfwd> and in the synopsis of other headers but it is well-formed to include both <iosfwd> and one or more of the other headers.290
[ Note: The class template specialization basic_ios<charT, traits> serves as a virtual base class for the class templates basic_istream, basic_ostream, and class templates derived from them. basic_iostream is a class template derived from both basic_istream<charT, traits> and basic_ostream<charT, traits>.
The class template specialization basic_streambuf<charT, traits> serves as a base class for class templates basic_stringbuf and basic_filebuf.
The class template specialization basic_istream<charT, traits> serves as a base class for class templates basic_istringstream and basic_ifstream.
The class template specialization basic_ostream<charT, traits> serves as a base class for class templates basic_ostringstream and basic_ofstream.
The class template specialization basic_iostream<charT, traits> serves as a base class for class templates basic_stringstream and basic_fstream.
Other typedef-names define instances of class templates specialized for char or wchar_t types.
Specializations of the class template fpos are used for specifying file position information.
The types streampos and wstreampos are used for positioning streams specialized on char and wchar_t respectively.
This synopsis suggests a circularity between streampos and char_traits<char>. An implementation can avoid this circularity by substituting equivalent types. One way to do this might be
template<class stateT> class fpos { ... }; // depends on nothing
using _STATE = ... ; // implementation private declaration of stateT
using streampos = fpos<_STATE>;
template<> struct char_traits<char> {
using pos_type = streampos;
}
— end note ]
It is the implementation's responsibility to implement headers so that including <iosfwd> and other headers does not violate the rules about multiple occurrences of default arguments.
#include <ios>
#include <streambuf>
#include <istream>
#include <ostream>
namespace std {
extern istream cin;
extern ostream cout;
extern ostream cerr;
extern ostream clog;
extern wistream wcin;
extern wostream wcout;
extern wostream wcerr;
extern wostream wclog;
}
In this Clause, the type name FILE refers to the type FILE declared in <cstdio> ([cstdio.syn]).
The header <iostream> declares objects that associate objects with the standard C streams provided for by the functions declared in <cstdio> ([c.files]), and includes all the headers necessary to use these objects.
The objects are constructed and the associations are established at some time prior to or during the first time an object of class ios_base::Init is constructed, and in any case before the body of main begins execution.291 The objects are not destroyed during program execution.292 The results of including <iostream> in a translation unit shall be as if <iostream> defined an instance of ios_base::Init with static storage duration.
Mixing operations on corresponding wide- and narrow-character streams follows the same semantics as mixing such operations on FILEs, as specified in the C standard library.
Concurrent access to a synchronized ([ios.members.static]) standard iostream object's formatted and unformatted input ([istream]) and output ([ostream]) functions or a standard C stream by multiple threads shall not result in a data race ([intro.multithread]). [ Note: Users must still synchronize concurrent use of these objects and streams by multiple threads if they wish to avoid interleaved characters. — end note ]
See also: ISO C 7.21.2.
If it is possible for them to do so, implementations are encouraged to initialize the objects earlier than required.
Constructors and destructors for static objects can access these objects to read input from stdin or write output to stdout or stderr.
The object cin controls input from a stream buffer associated with the object stdin, declared in <cstdio> ([cstdio.syn]).
After the object cin is initialized, cin.tie() returns &cout. Its state is otherwise the same as required for basic_ios<char>::init ([basic.ios.cons]).
The object cout controls output to a stream buffer associated with the object stdout, declared in <cstdio> ([cstdio.syn]).
The object cerr controls output to a stream buffer associated with the object stderr, declared in <cstdio> ([cstdio.syn]).
After the object cerr is initialized, cerr.flags() & unitbuf is nonzero and cerr.tie() returns &cout. Its state is otherwise the same as required for basic_ios<char>::init ([basic.ios.cons]).
The object clog controls output to a stream buffer associated with the object stderr, declared in <cstdio> ([cstdio.syn]).
The object wcin controls input from a stream buffer associated with the object stdin, declared in <cstdio> ([cstdio.syn]).
After the object wcin is initialized, wcin.tie() returns &wcout. Its state is otherwise the same as required for basic_ios<wchar_t>::init ([basic.ios.cons]).
The object wcout controls output to a stream buffer associated with the object stdout, declared in <cstdio> ([cstdio.syn]).
The object wcerr controls output to a stream buffer associated with the object stderr, declared in <cstdio> ([cstdio.syn]).
After the object wcerr is initialized, wcerr.flags() & unitbuf is nonzero and wcerr.tie() returns &wcout. Its state is otherwise the same as required for basic_ios<wchar_t>::init ([basic.ios.cons]).
The object wclog controls output to a stream buffer associated with the object stderr, declared in <cstdio> ([cstdio.syn]).
#include <iosfwd>
namespace std {
using streamoff = implementation-defined;
using streamsize = implementation-defined;
template <class stateT> class fpos;
class ios_base;
template <class charT, class traits = char_traits<charT>>
class basic_ios;
// [std.ios.manip], manipulators
ios_base& boolalpha (ios_base& str);
ios_base& noboolalpha(ios_base& str);
ios_base& showbase (ios_base& str);
ios_base& noshowbase (ios_base& str);
ios_base& showpoint (ios_base& str);
ios_base& noshowpoint(ios_base& str);
ios_base& showpos (ios_base& str);
ios_base& noshowpos (ios_base& str);
ios_base& skipws (ios_base& str);
ios_base& noskipws (ios_base& str);
ios_base& uppercase (ios_base& str);
ios_base& nouppercase(ios_base& str);
ios_base& unitbuf (ios_base& str);
ios_base& nounitbuf (ios_base& str);
// [adjustfield.manip], adjustfield
ios_base& internal (ios_base& str);
ios_base& left (ios_base& str);
ios_base& right (ios_base& str);
// [basefield.manip], basefield
ios_base& dec (ios_base& str);
ios_base& hex (ios_base& str);
ios_base& oct (ios_base& str);
// [floatfield.manip], floatfield
ios_base& fixed (ios_base& str);
ios_base& scientific (ios_base& str);
ios_base& hexfloat (ios_base& str);
ios_base& defaultfloat(ios_base& str);
// [error.reporting], error reporting
enum class io_errc {
stream = 1
};
template <> struct is_error_code_enum<io_errc> : public true_type { };
error_code make_error_code(io_errc e) noexcept;
error_condition make_error_condition(io_errc e) noexcept;
const error_category& iostream_category() noexcept;
}
using streamoff = implementation-defined;
The type streamoff is a synonym for one of the signed basic integral types of sufficient size to represent the maximum possible file size for the operating system.293
using streamsize = implementation-defined;
The type streamsize is a synonym for one of the signed basic integral types. It is used to represent the number of characters transferred in an I/O operation, or the size of I/O buffers.294
Typically long long.
streamsize is used in most places where ISO C would use size_t. Most of the uses of streamsize could use size_t, except for the strstreambuf constructors, which require negative values. It should probably be the signed type corresponding to size_t (which is what Posix.2 calls ssize_t).
namespace std {
class ios_base {
public:
class failure; // see below
// [ios::fmtflags], fmtflags
using fmtflags = T1;
static constexpr fmtflags boolalpha = unspecified;
static constexpr fmtflags dec = unspecified;
static constexpr fmtflags fixed = unspecified;
static constexpr fmtflags hex = unspecified;
static constexpr fmtflags internal = unspecified;
static constexpr fmtflags left = unspecified;
static constexpr fmtflags oct = unspecified;
static constexpr fmtflags right = unspecified;
static constexpr fmtflags scientific = unspecified;
static constexpr fmtflags showbase = unspecified;
static constexpr fmtflags showpoint = unspecified;
static constexpr fmtflags showpos = unspecified;
static constexpr fmtflags skipws = unspecified;
static constexpr fmtflags unitbuf = unspecified;
static constexpr fmtflags uppercase = unspecified;
static constexpr fmtflags adjustfield = see below;
static constexpr fmtflags basefield = see below;
static constexpr fmtflags floatfield = see below;
// [ios::iostate], iostate
using iostate = T2;
static constexpr iostate badbit = unspecified;
static constexpr iostate eofbit = unspecified;
static constexpr iostate failbit = unspecified;
static constexpr iostate goodbit = see below;
// [ios::openmode], openmode
using openmode = T3;
static constexpr openmode app = unspecified;
static constexpr openmode ate = unspecified;
static constexpr openmode binary = unspecified;
static constexpr openmode in = unspecified;
static constexpr openmode out = unspecified;
static constexpr openmode trunc = unspecified;
// [ios::seekdir], seekdir
using seekdir = T4;
static constexpr seekdir beg = unspecified;
static constexpr seekdir cur = unspecified;
static constexpr seekdir end = unspecified;
class Init;
// [fmtflags.state], fmtflags state
fmtflags flags() const;
fmtflags flags(fmtflags fmtfl);
fmtflags setf(fmtflags fmtfl);
fmtflags setf(fmtflags fmtfl, fmtflags mask);
void unsetf(fmtflags mask);
streamsize precision() const;
streamsize precision(streamsize prec);
streamsize width() const;
streamsize width(streamsize wide);
// [ios.base.locales], locales
locale imbue(const locale& loc);
locale getloc() const;
// [ios.base.storage], storage
static int xalloc();
long& iword(int index);
void*& pword(int index);
// destructor:
virtual ~ios_base();
// [ios.base.callback], callbacks;
enum event { erase_event, imbue_event, copyfmt_event };
using event_callback = void (*)(event, ios_base&, int index);
void register_callback(event_callback fn, int index);
ios_base(const ios_base&) = delete;
ios_base& operator=(const ios_base&) = delete;
static bool sync_with_stdio(bool sync = true);
protected:
ios_base();
private:
static int index; // exposition only
long* iarray; // exposition only
void** parray; // exposition only
};
}
ios_base defines several member types:
a type failure, defined as either a class derived from system_error or a synonym for a class derived from system_error;
a class Init;
three bitmask types, fmtflags, iostate, and openmode;
an enumerated type, seekdir.
It maintains several kinds of data:
state information that reflects the integrity of the stream buffer;
control information that influences how to interpret (format) input sequences and how to generate (format) output sequences;
additional information that is stored by the program for its private use.
[ Note: For the sake of exposition, the maintained data is presented here as:
static int index, specifies the next available unique index for the integer or pointer arrays maintained for the private use of the program, initialized to an unspecified value;
long* iarray, points to the first element of an arbitrary-length long array maintained for the private use of the program;
void** parray, points to the first element of an arbitrary-length pointer array maintained for the private use of the program.
— end note ]
namespace std {
class ios_base::failure : public system_error {
public:
explicit failure(const string& msg, const error_code& ec = io_errc::stream);
explicit failure(const char* msg, const error_code& ec = io_errc::stream);
};
}
An implementation is permitted to define ios_base::failure as a synonym for a class with equivalent functionality to class ios_base::failure shown in this subclause. [ Note: When ios_base::failure is a synonym for another type it shall provide a nested type failure, to emulate the injected class name. — end note ] The class failure defines the base class for the types of all objects thrown as exceptions, by functions in the iostreams library, to report errors detected during stream buffer operations.
When throwing ios_base::failure exceptions, implementations should provide values of ec that identify the specific reason for the failure. [ Note: Errors arising from the operating system would typically be reported as system_category() errors with an error value of the error number reported by the operating system. Errors arising from within the stream library would typically be reported as error_code(io_errc::stream, iostream_category()). — end note ]
explicit failure(const string& msg, const error_code& ec = io_errc::stream);
Effects: Constructs an object of class failure by constructing the base class with msg and ec.
explicit failure(const char* msg, const error_code& ec = io_errc::stream);
Effects: Constructs an object of class failure by constructing the base class with msg and ec.
The type fmtflags is a bitmask type ([bitmask.types]). Setting its elements has the effects indicated in Table [tab:iostreams.fmtflags.effects].
| Element | Effect(s) if set |
| boolalpha | insert and extract bool type in alphabetic format |
| dec | converts integer input or generates integer output in decimal base |
| fixed | generate floating-point output in fixed-point notation |
| hex | converts integer input or generates integer output in hexadecimal base |
| internal | adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated |
| left | adds fill characters on the right (final positions) of certain generated output |
| oct | converts integer input or generates integer output in octal base |
| right | adds fill characters on the left (initial positions) of certain generated output |
| scientific | generates floating-point output in scientific notation |
| showbase | generates a prefix indicating the numeric base of generated integer output |
| showpoint | generates a decimal-point character unconditionally in generated floating-point output |
| showpos | generates a + sign in non-negative generated numeric output |
| skipws | skips leading whitespace before certain input operations |
| unitbuf | flushes output after each output operation |
| uppercase | replaces certain lowercase letters with their uppercase equivalents in generated output |
Type fmtflags also defines the constants indicated in Table [tab:iostreams.fmtflags.constants].
| Constant | Allowable values |
| adjustfield | left | right | internal |
| basefield | dec | oct | hex |
| floatfield | scientific | fixed |
The type iostate is a bitmask type ([bitmask.types]) that contains the elements indicated in Table [tab:iostreams.iostate.effects].
| Element | Effect(s) if set |
| badbit | indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file); |
| eofbit | indicates that an input operation reached the end of an input sequence; |
| failbit | indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters. |
The type openmode is a bitmask type ([bitmask.types]). It contains the elements indicated in Table [tab:iostreams.openmode.effects].
| Element | Effect(s) if set |
| app | seek to end before each write |
| ate | open and seek to end immediately after opening |
| binary | perform input and output in binary mode (as opposed to text mode) |
| in | open for input |
| out | open for output |
| trunc | truncate an existing stream when opening |
The type seekdir is an enumerated type ([enumerated.types]) that contains the elements indicated in Table [tab:iostreams.seekdir.effects].
| Element | Meaning |
| beg | request a seek (for subsequent input or output) relative to the beginning of the stream |
| cur | request a seek relative to the current position within the sequence |
| end | request a seek relative to the current end of the sequence |
namespace std {
class ios_base::Init {
public:
Init();
~Init();
private:
static int init_cnt; // exposition only
};
}
The class Init describes an object whose construction ensures the construction of the eight objects declared in <iostream> ([iostream.objects]) that associate file stream buffers with the standard C streams provided for by the functions declared in <cstdio> ([cstdio.syn]).
For the sake of exposition, the maintained data is presented here as:
static int init_cnt, counts the number of constructor and destructor calls for class Init, initialized to zero.
Effects: Constructs an object of class Init. Constructs and initializes the objects cin, cout, cerr, clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.
Returns: The format control information for both input and output.
fmtflags flags(fmtflags fmtfl);
Postconditions: fmtfl == flags().
Returns: The previous value of flags().
fmtflags setf(fmtflags fmtfl);
Effects: Sets fmtfl in flags().
Returns: The previous value of flags().
fmtflags setf(fmtflags fmtfl, fmtflags mask);
Effects: Clears mask in flags(), sets fmtfl & mask in flags().
Returns: The previous value of flags().
Effects: Clears mask in flags().
Returns: The precision to generate on certain output conversions.
streamsize precision(streamsize prec);
Postconditions: prec == precision().
Returns: The previous value of precision().
Returns: The minimum field width (number of characters) to generate on certain output conversions.
streamsize width(streamsize wide);
Postconditions: wide == width().
Returns: The previous value of width().
locale imbue(const locale& loc);
Effects: Calls each registered callback pair (fn, index) ([ios.base.callback]) as (*fn)(imbue_event, *this, index) at such a time that a call to ios_base::getloc() from within fn returns the new locale value loc.
Returns: The previous value of getloc().
Postconditions: loc == getloc().
Returns: If no locale has been imbued, a copy of the global C++ locale, locale(), in effect at the time of construction. Otherwise, returns the imbued locale, to be used to perform locale-dependent input and output operations.
bool sync_with_stdio(bool sync = true);
Returns: true if the previous state of the standard iostream objects ([iostream.objects]) was synchronized and otherwise returns false. The first time it is called, the function returns true.
When a standard iostream object str is synchronized with a standard stdio stream f, the effect of inserting a character c by
fputc(f, c);
is the same as the effect of
str.rdbuf()->sputc(c);
for any sequences of characters; the effect of extracting a character c by
c = fgetc(f);
is the same as the effect of
c = str.rdbuf()->sbumpc();
for any sequences of characters; and the effect of pushing back a character c by
ungetc(c, f);
is the same as the effect of
str.rdbuf()->sputbackc(c);
for any sequence of characters.295
This implies that operations on a standard iostream object can be mixed arbitrarily with operations on the corresponding stdio stream. In practical terms, synchronization usually means that a standard iostream object and a standard stdio object share a buffer.
Returns: index ++.
Remarks: Concurrent access to this function by multiple threads shall not result in a data race ([intro.multithread]).
Effects: If iarray is a null pointer, allocates an array of long of unspecified size and stores a pointer to its first element in iarray. The function then extends the array pointed at by iarray as necessary to include the element iarray[idx]. Each newly allocated element of the array is initialized to zero. The reference returned is invalid after any other operations on the object.296 However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling iword with the same index yields another reference to the same value. If the function fails297 and *this is a base subobject of a basic_ios<> object or subobject, the effect is equivalent to calling basic_ios<>::setstate(badbit) on the derived object (which may throw failure).
Returns: On success iarray[idx]. On failure, a valid long& initialized to 0.
Effects: If parray is a null pointer, allocates an array of pointers to void of unspecified size and stores a pointer to its first element in parray. The function then extends the array pointed at by parray as necessary to include the element parray[idx]. Each newly allocated element of the array is initialized to a null pointer. The reference returned is invalid after any other operations on the object. However, the value of the storage referred to is retained, so that until the next call to copyfmt, calling pword with the same index yields another reference to the same value. If the function fails298 and *this is a base subobject of a basic_ios<> object or subobject, the effect is equivalent to calling basic_ios<>::setstate(badbit) on the derived object (which may throw failure).
Returns: On success parray[idx]. On failure a valid void*& initialized to 0.
Remarks: After a subsequent call to pword(int) for the same object, the earlier return value may no longer be valid.
An implementation is free to implement both the integer array pointed at by iarray and the pointer array pointed at by parray as sparse data structures, possibly with a one-element cache for each.
for example, because it cannot allocate space.
for example, because it cannot allocate space.
void register_callback(event_callback fn, int index);
Effects: Registers the pair (fn, index) such that during calls to imbue() ([ios.base.locales]), copyfmt(), or ~ios_base() ([ios.base.cons]), the function fn is called with argument index. Functions registered are called when an event occurs, in opposite order of registration. Functions registered while a callback function is active are not called until the next event.
Requires: The function fn shall not throw exceptions.
Remarks: Identical pairs are not merged. A function registered twice will be called twice.
Effects: Each ios_base member has an indeterminate value after construction. The object's members shall be initialized by calling basic_ios::init before the object's first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.
Effects: Destroys an object of class ios_base. Calls each registered callback pair (fn, index) ([ios.base.callback]) as (*fn)(erase_event, *this, index) at such time that any ios_base member function called from within fn has well defined results.
namespace std {
template <class stateT> class fpos {
public:
// [fpos.members], members
stateT state() const;
void state(stateT);
private;
stateT st; // exposition only
};
}
Operations specified in Table [tab:iostreams.position.requirements] are permitted. In that table,
P refers to an instance of fpos,
p and q refer to values of type P,
O refers to type streamoff,
o refers to a value of type streamoff,
sz refers to a value of type streamsize and
i refers to a value of type int.
| Expression | Return type | Operational | Assertion/note |
| semantics | pre-/post-condition | ||
| P(i) |
p == P(i) note: a destructor is assumed. | ||
|
P p(i); P p = i; | post: p == P(i). | ||
| P(o) | fpos | converts from offset | |
| O(p) | streamoff | converts to offset | P(O(p)) == p |
| p == q | convertible to bool | == is an equivalence relation | |
| p != q | convertible to bool | !(p == q) | |
|
q = p + o p += o | fpos | + offset | q - o == p |
|
q = p - o p -= o | fpos | - offset | q + o == p |
| o = p - q | streamoff | distance | q + o == p |
|
streamsize(o) O(sz) |
streamsize streamoff |
converts converts |
streamsize(O(sz)) == sz streamsize(O(sz)) == sz |
[ Note: Every implementation is required to supply overloaded operators on fpos objects to satisfy the requirements of [fpos.operations]. It is unspecified whether these operators are members of fpos, global operators, or provided in some other way. — end note ]
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ios : public ios_base {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [iostate.flags], flags functions
explicit operator bool() const;
bool operator!() const;
iostate rdstate() const;
void clear(iostate state = goodbit);
void setstate(iostate state);
bool good() const;
bool eof() const;
bool fail() const;
bool bad() const;
iostate exceptions() const;
void exceptions(iostate except);
// [basic.ios.cons], constructor/destructor
explicit basic_ios(basic_streambuf<charT, traits>* sb);
virtual ~basic_ios();
// [basic.ios.members], members
basic_ostream<charT, traits>* tie() const;
basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);
basic_streambuf<charT, traits>* rdbuf() const;
basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);
basic_ios& copyfmt(const basic_ios& rhs);
char_type fill() const;
char_type fill(char_type ch);
locale imbue(const locale& loc);
char narrow(char_type c, char dfault) const;
char_type widen(char c) const;
basic_ios(const basic_ios&) = delete;
basic_ios& operator=(const basic_ios&) = delete;
protected:
basic_ios();
void init(basic_streambuf<charT, traits>* sb);
void move(basic_ios& rhs);
void move(basic_ios&& rhs);
void swap(basic_ios& rhs) noexcept;
void set_rdbuf(basic_streambuf<charT, traits>* sb);
};
}
explicit basic_ios(basic_streambuf<charT, traits>* sb);
Effects: Constructs an object of class basic_ios, assigning initial values to its member objects by calling init(sb).
Effects: Constructs an object of class basic_ios ([ios.base.cons]) leaving its member objects uninitialized. The object shall be initialized by calling basic_ios::init before its first use or before it is destroyed, whichever comes first; otherwise the behavior is undefined.
Remarks: The destructor does not destroy rdbuf().
void init(basic_streambuf<charT, traits>* sb);
Postconditions: The postconditions of this function are indicated in Table [tab:iostreams.basicios.init.effects].
| Element | Value |
| rdbuf() | sb |
| tie() | 0 |
| rdstate() | goodbit if sb is not a null pointer, otherwise badbit. |
| exceptions() | goodbit |
| flags() | skipws | dec |
| width() | 0 |
| precision() | 6 |
| fill() | widen(' '); |
| getloc() | a copy of the value returned by locale() |
| iarray | a null pointer |
| parray | a null pointer |
basic_ostream<charT, traits>* tie() const;
Returns: An output sequence that is tied to (synchronized with) the sequence controlled by the stream buffer.
basic_ostream<charT, traits>* tie(basic_ostream<charT, traits>* tiestr);
Requires: If tiestr is not null, tiestr must not be reachable by traversing the linked list of tied stream objects starting from tiestr->tie().
Postconditions: tiestr == tie().
Returns: The previous value of tie().
basic_streambuf<charT, traits>* rdbuf() const;
Returns: A pointer to the streambuf associated with the stream.
basic_streambuf<charT, traits>* rdbuf(basic_streambuf<charT, traits>* sb);
Postconditions: sb == rdbuf().
Effects: Calls clear().
Returns: The previous value of rdbuf().
locale imbue(const locale& loc);
Effects: Calls ios_base::imbue(loc) ([ios.base.locales]) and if rdbuf() != 0 then rdbuf()->pubimbue(loc) ([streambuf.locales]).
Returns: The prior value of ios_base::imbue().
char narrow(char_type c, char dfault) const;
Returns: use_facet<ctype<char_type>>(getloc()).narrow(c, dfault)
char_type widen(char c) const;
Returns: use_facet<ctype<char_type>>(getloc()).widen(c)
Returns: The character used to pad (fill) an output conversion to the specified field width.
char_type fill(char_type fillch);
Postconditions: traits::eq(fillch, fill())
Returns: The previous value of fill().
basic_ios& copyfmt(const basic_ios& rhs);
Effects: If (this == &rhs) does nothing. Otherwise assigns to the member objects of *this the corresponding member objects of rhs as follows:
calls each registered callback pair (fn, index) as (*fn)(erase_event, *this, index);
assigns to the member objects of *this the corresponding member objects of rhs, except that
rdstate(), rdbuf(), and exceptions() are left unchanged;
the contents of arrays pointed at by pword and iword are copied, not the pointers themselves;299 and
if any newly stored pointer values in *this point at objects stored outside the object rhs and those objects are destroyed when rhs is destroyed, the newly stored pointer values are altered to point at newly constructed copies of the objects;
calls each callback pair that was copied from rhs as (*fn)(copyfmt_event, *this, index);
calls exceptions(rhs.exceptions()).
Note: The second pass through the callback pairs permits a copied pword value to be zeroed, or to have its referent deep copied or reference counted, or to have other special action taken.
Postconditions: The postconditions of this function are indicated in Table [tab:iostreams.copyfmt.effects].
| Element | Value |
| rdbuf() | unchanged |
| tie() | rhs.tie() |
| rdstate() | unchanged |
| exceptions() | rhs.exceptions() |
| flags() | rhs.flags() |
| width() | rhs.width() |
| precision() | rhs.precision() |
| fill() | rhs.fill() |
| getloc() | rhs.getloc() |
Returns: *this.
void move(basic_ios& rhs);
void move(basic_ios&& rhs);
Postconditions: *this shall have the state that rhs had before the function call, except that rdbuf() shall return 0. rhs shall be in a valid but unspecified state, except that rhs.rdbuf() shall return the same value as it returned before the function call, and rhs.tie() shall return 0.
void swap(basic_ios& rhs) noexcept;
Effects: The states of *this and rhs shall be exchanged, except that rdbuf() shall return the same value as it returned before the function call, and rhs.rdbuf() shall return the same value as it returned before the function call.
void set_rdbuf(basic_streambuf<charT, traits>* sb);
Requires: sb != nullptr.
Effects: Associates the basic_streambuf object pointed to by sb with this stream without calling clear().
Postconditions: rdbuf() == sb.
Throws: Nothing.
This suggests an infinite amount of copying, but the implementation can keep track of the maximum element of the arrays that is nonzero.
explicit operator bool() const;
Returns: !fail().
Returns: fail().
Returns: The error state of the stream buffer.
void clear(iostate state = goodbit);
Postconditions: If rdbuf() != 0 then state == rdstate(); otherwise rdstate() == (state | ios_base::badbit).
Effects: If ((state | (rdbuf() ? goodbit : badbit)) & exceptions()) == 0, returns. Otherwise, the function throws an object of class basic_ios::failure ([ios::failure]), constructed with implementation-defined argument values.
Effects: Calls clear(rdstate() | state) (which may throw basic_ios::failure ([ios::failure])).
Returns: rdstate() == 0
Returns: true if eofbit is set in rdstate().
Returns: true if badbit is set in rdstate().
Returns: A mask that determines what elements set in rdstate() cause exceptions to be thrown.
void exceptions(iostate except);
Postconditions: except == exceptions().
Effects: Calls clear(rdstate()).
Checking badbit also for fail() is historical practice.
ios_base& boolalpha(ios_base& str);
Effects: Calls str.setf(ios_base::boolalpha).
Returns: str.
ios_base& noboolalpha(ios_base& str);
Effects: Calls str.unsetf(ios_base::boolalpha).
Returns: str.
ios_base& showbase(ios_base& str);
Effects: Calls str.setf(ios_base::showbase).
Returns: str.
ios_base& noshowbase(ios_base& str);
Effects: Calls str.unsetf(ios_base::showbase).
Returns: str.
ios_base& showpoint(ios_base& str);
Effects: Calls str.setf(ios_base::showpoint).
Returns: str.
ios_base& noshowpoint(ios_base& str);
Effects: Calls str.unsetf(ios_base::showpoint).
Returns: str.
ios_base& showpos(ios_base& str);
Effects: Calls str.setf(ios_base::showpos).
Returns: str.
ios_base& noshowpos(ios_base& str);
Effects: Calls str.unsetf(ios_base::showpos).
Returns: str.
ios_base& skipws(ios_base& str);
Effects: Calls str.setf(ios_base::skipws).
Returns: str.
ios_base& noskipws(ios_base& str);
Effects: Calls str.unsetf(ios_base::skipws).
Returns: str.
ios_base& uppercase(ios_base& str);
Effects: Calls str.setf(ios_base::uppercase).
Returns: str.
ios_base& nouppercase(ios_base& str);
Effects: Calls str.unsetf(ios_base::uppercase).
Returns: str.
ios_base& unitbuf(ios_base& str);
Effects: Calls str.setf(ios_base::unitbuf).
Returns: str.
ios_base& nounitbuf(ios_base& str);
Effects: Calls str.unsetf(ios_base::unitbuf).
Returns: str.
ios_base& internal(ios_base& str);
Effects: Calls str.setf(ios_base::internal, ios_base::adjustfield).
Returns: str.
ios_base& left(ios_base& str);
Effects: Calls str.setf(ios_base::left, ios_base::adjustfield).
Returns: str.
ios_base& right(ios_base& str);
Effects: Calls str.setf(ios_base::right, ios_base::adjustfield).
Returns: str.
Effects: Calls str.setf(ios_base::dec, ios_base::basefield).
Effects: Calls str.setf(ios_base::hex, ios_base::basefield).
Returns: str.
Effects: Calls str.setf(ios_base::oct, ios_base::basefield).
Returns: str.
The function signature dec(ios_base&) can be called by the function signature basic_ostream& stream::operator<<(ios_base& (*)(ios_base&)) to permit expressions of the form cout << dec to change the format flags stored in cout.
ios_base& fixed(ios_base& str);
Effects: Calls str.setf(ios_base::fixed, ios_base::floatfield).
Returns: str.
ios_base& scientific(ios_base& str);
Effects: Calls str.setf(ios_base::scientific, ios_base::floatfield).
Returns: str.
ios_base& hexfloat(ios_base& str);
Effects: Calls str.setf(ios_base::fixed | ios_base::scientific, ios_base::floatfield).
Returns: str.
[ Note: The more obvious use of ios_base::hex to specify hexadecimal floating-point format would change the meaning of existing well defined programs. C++ 2003 gives no meaning to the combination of fixed and scientific. — end note ]
Effects: Calls str.unsetf(ios_base::floatfield).
Returns: str.
error_code make_error_code(io_errc e) noexcept;
Returns: error_code(static_cast<int>(e), iostream_category()).
error_condition make_error_condition(io_errc e) noexcept;
Returns: error_condition(static_cast<int>(e), iostream_category()).
const error_category& iostream_category() noexcept;
Returns: A reference to an object of a type derived from class error_category.
The object's default_error_condition and equivalent virtual functions shall behave as specified for the class error_category. The object's name virtual function shall return a pointer to the string "iostream".
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_streambuf;
using streambuf = basic_streambuf<char>;
using wstreambuf = basic_streambuf<wchar_t>;
}
The header <streambuf> defines types that control input from and output to character sequences.
Stream buffers can impose various constraints on the sequences they control. Some constraints are:
The controlled input sequence can be not readable.
The controlled output sequence can be not writable.
The controlled sequences can be associated with the contents of other representations for character sequences, such as external files.
The controlled sequences can support operations directly to or from associated sequences.
The controlled sequences can impose limitations on how the program can read characters from a sequence, write characters to a sequence, put characters back into an input sequence, or alter the stream position.
Each sequence is characterized by three pointers which, if non-null, all point into the same charT array object. The array object represents, at any moment, a (sub)sequence of characters from the sequence. Operations performed on a sequence alter the values stored in these pointers, perform reads and writes directly to or from associated sequences, and alter “the stream position” and conversion state as needed to maintain this subsequence relationship. The three pointers are:
the beginning pointer, or lowest element address in the array (called xbeg here);
the next pointer, or next element address that is a current candidate for reading or writing (called xnext here);
the end pointer, or first element address beyond the end of the array (called xend here).
The following semantic constraints shall always apply for any set of three pointers for a sequence, using the pointer names given immediately above:
If xnext is not a null pointer, then xbeg and xend shall also be non-null pointers into the same charT array, as described above; otherwise, xbeg and xend shall also be null.
If xnext is not a null pointer and xnext < xend for an output sequence, then a write position is available. In this case, *xnext shall be assignable as the next element to write (to put, or to store a character value, into the sequence).
If xnext is not a null pointer and xbeg < xnext for an input sequence, then a putback position is available. In this case, xnext[-1] shall have a defined value and is the next (preceding) element to store a character that is put back into the input sequence.
If xnext is not a null pointer and xnext < xend for an input sequence, then a read position is available. In this case, *xnext shall have a defined value and is the next element to read (to get, or to obtain a character value, from the sequence).
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_streambuf {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
virtual ~basic_streambuf();
// [streambuf.locales], locales
locale pubimbue(const locale& loc);
locale getloc() const;
// [streambuf.buffer], buffer and positioning
basic_streambuf* pubsetbuf(char_type* s, streamsize n);
pos_type pubseekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
pos_type pubseekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out);
int pubsync();
// Get and put areas
// [streambuf.pub.get], get area
streamsize in_avail();
int_type snextc();
int_type sbumpc();
int_type sgetc();
streamsize sgetn(char_type* s, streamsize n);
// [streambuf.pub.pback], putback
int_type sputbackc(char_type c);
int_type sungetc();
// [streambuf.pub.put], put area
int_type sputc(char_type c);
streamsize sputn(const char_type* s, streamsize n);
protected:
basic_streambuf();
basic_streambuf(const basic_streambuf& rhs);
basic_streambuf& operator=(const basic_streambuf& rhs);
void swap(basic_streambuf& rhs);
// [streambuf.get.area], get area access
char_type* eback() const;
char_type* gptr() const;
char_type* egptr() const;
void gbump(int n);
void setg(char_type* gbeg, char_type* gnext, char_type* gend);
// [streambuf.put.area], put area access
char_type* pbase() const;
char_type* pptr() const;
char_type* epptr() const;
void pbump(int n);
void setp(char_type* pbeg, char_type* pend);
// [streambuf.virtuals], virtual functions
// [streambuf.virt.locales], locales
virtual void imbue(const locale& loc);
// [streambuf.virt.buffer], buffer management and positioning
virtual basic_streambuf* setbuf(char_type* s, streamsize n);
virtual pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
virtual pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out);
virtual int sync();
// [streambuf.virt.get], get area
virtual streamsize showmanyc();
virtual streamsize xsgetn(char_type* s, streamsize n);
virtual int_type underflow();
virtual int_type uflow();
// [streambuf.virt.pback], putback
virtual int_type pbackfail(int_type c = traits::eof());
// [streambuf.virt.put], put area
virtual streamsize xsputn(const char_type* s, streamsize n);
virtual int_type overflow(int_type c = traits::eof());
};
}
The class template basic_streambuf serves as an abstract base class for deriving various stream buffers whose objects each control two character sequences:
a character input sequence;
a character output sequence.
Remarks: Once the getloc() member is initialized, results of calling locale member functions, and of members of facets so obtained, can safely be cached until the next time the member imbue is called.
basic_streambuf(const basic_streambuf& rhs);
Effects: Constructs a copy of rhs.
Effects: None.
The default constructor is protected for class basic_streambuf to assure that only objects for classes derived from this class may be constructed.
locale pubimbue(const locale& loc);
Postconditions: loc == getloc().
Effects: Calls imbue(loc).
Returns: Previous value of getloc().
Returns: If pubimbue() has ever been called, then the last value of loc supplied, otherwise the current global locale, locale(), in effect at the time of construction. If called after pubimbue() has been called but before pubimbue has returned (i.e., from within the call of imbue()) then it returns the previous value.
basic_streambuf* pubsetbuf(char_type* s, streamsize n);
Returns: setbuf(s, n).
pos_type pubseekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
Returns: seekoff(off, way, which).
pos_type pubseekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out);
Returns: seekpos(sp, which).
Returns: sync().
Returns: If a read position is available, returns egptr() - gptr(). Otherwise returns showmanyc() ([streambuf.virt.get]).
Effects: Calls sbumpc().
Returns: If that function returns traits::eof(), returns traits::eof(). Otherwise, returns sgetc().
Returns: If the input sequence read position is not available, returns uflow(). Otherwise, returns traits::to_int_type(*gptr()) and increments the next pointer for the input sequence.
Returns: If the input sequence read position is not available, returns underflow(). Otherwise, returns traits::to_int_type(*gptr()).
streamsize sgetn(char_type* s, streamsize n);
Returns: xsgetn(s, n).
int_type sputbackc(char_type c);
Returns: If the input sequence putback position is not available, or if traits::eq(c, gptr()[-1]) is false, returns pbackfail(traits::to_int_type(c)). Otherwise, decrements the next pointer for the input sequence and returns traits::to_int_type(*gptr()).
Returns: If the input sequence putback position is not available, returns pbackfail(). Otherwise, decrements the next pointer for the input sequence and returns traits::to_int_type(*gptr()).
Returns: If the output sequence write position is not available, returns overflow(traits::to_int_type(c)). Otherwise, stores c at the next pointer for the output sequence, increments the pointer, and returns traits::to_int_type(c).
streamsize sputn(const char_type* s, streamsize n);
Returns: xsputn(s, n).
basic_streambuf& operator=(const basic_streambuf& rhs);
Effects: Assigns the data members of rhs to *this.
Returns: *this.
void swap(basic_streambuf& rhs);
Effects: Swaps the data members of rhs and *this.
Returns: The beginning pointer for the input sequence.
Returns: The next pointer for the input sequence.
Returns: The end pointer for the input sequence.
Effects: Adds n to the next pointer for the input sequence.
void setg(char_type* gbeg, char_type* gnext, char_type* gend);
Postconditions: gbeg == eback(), gnext == gptr(), and gend == egptr().
Returns: The beginning pointer for the output sequence.
Returns: The next pointer for the output sequence.
Returns: The end pointer for the output sequence.
Effects: Adds n to the next pointer for the output sequence.
void setp(char_type* pbeg, char_type* pend);
Postconditions: pbeg == pbase(), pbeg == pptr(), and pend == epptr().
Effects: Change any translations based on locale.
Remarks: Allows the derived class to be informed of changes in locale at the time they occur. Between invocations of this function a class derived from streambuf can safely cache results of calls to locale functions and to members of facets so obtained.
Default behavior: Does nothing.
basic_streambuf* setbuf(char_type* s, streamsize n);
Effects: Influences stream buffering in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf.virtuals], [filebuf.virtuals]).
Default behavior: Does nothing. Returns this.
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out);
Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf.virtuals], [filebuf.virtuals]).
Default behavior: Returns pos_type(off_type(-1)).
pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out);
Effects: Alters the stream positions within one or more of the controlled sequences in a way that is defined separately for each class derived from basic_streambuf in this Clause ([stringbuf], [filebuf]).
Default behavior: Returns pos_type(off_type(-1)).
Effects: Synchronizes the controlled sequences with the arrays. That is, if pbase() is non-null the characters between pbase() and pptr() are written to the controlled sequence. The pointers may then be reset as appropriate.
Returns: -1 on failure. What constitutes failure is determined by each derived class ([filebuf.virtuals]).
Default behavior: Returns zero.
streamsize showmanyc();303
Returns: An estimate of the number of characters available in the sequence, or -1. If it returns a positive value, then successive calls to underflow() will not return traits::eof() until at least that number of characters have been extracted from the stream. If showmanyc() returns -1, then calls to underflow() or uflow() will fail.304
Default behavior: Returns zero.
Remarks: Uses traits::eof().
streamsize xsgetn(char_type* s, streamsize n);
Effects: Assigns up to n characters to successive elements of the array whose first element is designated by s. The characters assigned are read from the input sequence as if by repeated calls to sbumpc(). Assigning stops when either n characters have been assigned or a call to sbumpc() would return traits::eof().
Remarks: Uses traits::eof().
Remarks: The public members of basic_streambuf call this virtual function only if gptr() is null or gptr() >= egptr()
Returns: traits::to_int_type(c), where c is the first character of the pending sequence, without moving the input sequence position past it. If the pending sequence is null then the function returns traits::eof() to indicate failure.
The pending sequence of characters is defined as the concatenation of
the empty sequence if gptr() is null, otherwise the egptr() - gptr() characters starting at gptr(), followed by
some (possibly empty) sequence of characters read from the input sequence.
The result character is the first character of the pending sequence if it is non-empty, otherwise the next character that would be read from the input sequence.
The backup sequence is the empty sequence if eback() is null, otherwise the gptr() - eback() characters beginning at eback().
Effects: The function sets up the gptr() and egptr() such that if the pending sequence is non-empty, then egptr() is non-null and egptr() - gptr() characters starting at gptr() are the characters in the pending sequence, otherwise either gptr() is null or gptr() == egptr().
If eback() and gptr() are non-null then the function is not constrained as to their contents, but the “usual backup condition” is that either
the backup sequence contains at least gptr() - eback() characters, in which case the gptr() - eback() characters starting at eback() agree with the last gptr() - eback() characters of the backup sequence, or
the n characters starting at gptr() - n agree with the backup sequence (where n is the length of the backup sequence).
Default behavior: Returns traits::eof().
Requires: The constraints are the same as for underflow(), except that the result character shall be transferred from the pending sequence to the backup sequence, and the pending sequence shall not be empty before the transfer.
Default behavior: Calls underflow(). If underflow() returns traits::eof(), returns traits::eof(). Otherwise, returns the value of traits::to_int_type(*gptr()) and increment the value of the next pointer for the input sequence.
Returns: traits::eof() to indicate failure.
The morphemes of showmanyc are “es-how-many-see”, not “show-manic”.
underflow or uflow might fail by throwing an exception prematurely. The intention is not only that the calls will not return eof() but that they will return “immediately.”
Classes derived from basic_streambuf can provide more efficient ways to implement xsgetn() and xsputn() by overriding these definitions from the base class.
int_type pbackfail(int_type c = traits::eof());
Remarks: The public functions of basic_streambuf call this virtual function only when gptr() is null, gptr() == eback(), or traits::eq(traits::to_char_type(c), gptr()[-1]) returns false. Other calls shall also satisfy that constraint.
The pending sequence is defined as for underflow(), with the modifications that
If traits::eq_int_type(c, traits::eof()) returns true, then the input sequence is backed up one character before the pending sequence is determined.
If traits::eq_int_type(c, traits::eof()) returns false, then c is prepended. Whether the input sequence is backed up or modified in any other way is unspecified.
Postconditions: On return, the constraints of gptr(), eback(), and pptr() are the same as for underflow().
Returns: traits::eof() to indicate failure. Failure may occur because the input sequence could not be backed up, or if for some other reason the pointers could not be set consistent with the constraints. pbackfail() is called only when put back has really failed.
Returns some value other than traits::eof() to indicate success.
Default behavior: Returns traits::eof().
streamsize xsputn(const char_type* s, streamsize n);
Effects: Writes up to n characters to the output sequence as if by repeated calls to sputc(c). The characters written are obtained from successive elements of the array whose first element is designated by s. Writing stops when either n characters have been written or a call to sputc(c) would return traits::eof(). It is unspecified whether the function calls overflow() when pptr() == epptr() becomes true or whether it achieves the same effects by other means.
Returns: The number of characters written.
int_type overflow(int_type c = traits::eof());
Effects: Consumes some initial subsequence of the characters of the pending sequence. The pending sequence is defined as the concatenation of
the empty sequence if pbase() is not null, otherwise the pptr() - pbase() characters beginning at pbase(), followed by
the empty sequence if traits::eq_int_type(c, traits::eof()) returns true, otherwise the sequence consisting of c.
Remarks: The member functions sputc() and sputn() call this function in case that no room can be found in the put buffer enough to accommodate the argument character sequence.
Requires: Every overriding definition of this virtual function shall obey the following constraints:
The effect of consuming a character on the associated output sequence is specified306
Let r be the number of characters in the pending sequence not consumed. If r is nonzero then pbase() and pptr() shall be set so that: pptr() - pbase() == r and the r characters starting at pbase() are the associated output stream. In case r is zero (all characters of the pending sequence have been consumed) then either pbase() is set to nullptr, or pbase() and pptr() are both set to the same non-null value.
The function may fail if either appending some character to the associated output stream fails or if it is unable to establish pbase() and pptr() according to the above rules.
Returns: traits::eof() or throws an exception if the function fails.
Otherwise, returns some value other than traits::eof() to indicate success.307
Default behavior: Returns traits::eof().
That is, for each class derived from an instance of basic_streambuf in this Clause ([stringbuf], [filebuf]), a specification of how consuming a character effects the associated output sequence is given. There is no requirement on a program-defined class.
Typically, overflow returns c to indicate success, except when traits::eq_int_type(c, traits::eof()) returns true, in which case it returns traits::not_eof(c).
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_istream;
using istream = basic_istream<char>;
using wistream = basic_istream<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_iostream;
using iostream = basic_iostream<char>;
using wiostream = basic_iostream<wchar_t>;
template <class charT, class traits>
basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);
template <class charT, class traits, class T>
basic_istream<charT, traits>&
operator>>(basic_istream<charT, traits>&& is, T&& x);
}
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ostream;
using ostream = basic_ostream<char>;
using wostream = basic_ostream<wchar_t>;
template <class charT, class traits>
basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
template <class charT, class traits>
basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
template <class charT, class traits>
basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);
template <class charT, class traits, class T>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>&& os, const T& x);
}
namespace std {
// types T1, T2, ... are unspecified implementation types
T1 resetiosflags(ios_base::fmtflags mask);
T2 setiosflags (ios_base::fmtflags mask);
T3 setbase(int base);
template<charT> T4 setfill(charT c);
T5 setprecision(int n);
T6 setw(int n);
template <class moneyT> T7 get_money(moneyT& mon, bool intl = false);
template <class moneyT> T8 put_money(const moneyT& mon, bool intl = false);
template <class charT> T9 get_time(struct tm* tmb, const charT* fmt);
template <class charT> T10 put_time(const struct tm* tmb, const charT* fmt);
template <class charT>
T11 quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'));
template <class charT, class traits, class Allocator>
T12 quoted(const basic_string<charT, traits, Allocator>& s,
charT delim = charT('"'), charT escape = charT('\\'));
template <class charT, class traits, class Allocator>
T13 quoted(basic_string<charT, traits, Allocator>& s,
charT delim = charT('"'), charT escape = charT('\\'));
}
The header <istream> defines two types and a function signature that control input from a stream buffer along with a function template that extracts from stream rvalues.
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_istream
: virtual public basic_ios<charT, traits> {
public:
// types (inherited from basic_ios ([ios])):
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [istream.cons], constructor/destructor
explicit basic_istream(basic_streambuf<charT, traits>* sb);
virtual ~basic_istream();
// [istream::sentry], prefix/suffix
class sentry;
// [istream.formatted], formatted input
basic_istream<charT, traits>& operator>>(
basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&));
basic_istream<charT, traits>& operator>>(
basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
basic_istream<charT, traits>& operator>>(
ios_base& (*pf)(ios_base&));
basic_istream<charT, traits>& operator>>(bool& n);
basic_istream<charT, traits>& operator>>(short& n);
basic_istream<charT, traits>& operator>>(unsigned short& n);
basic_istream<charT, traits>& operator>>(int& n);
basic_istream<charT, traits>& operator>>(unsigned int& n);
basic_istream<charT, traits>& operator>>(long& n);
basic_istream<charT, traits>& operator>>(unsigned long& n);
basic_istream<charT, traits>& operator>>(long long& n);
basic_istream<charT, traits>& operator>>(unsigned long long& n);
basic_istream<charT, traits>& operator>>(float& f);
basic_istream<charT, traits>& operator>>(double& f);
basic_istream<charT, traits>& operator>>(long double& f);
basic_istream<charT, traits>& operator>>(void*& p);
basic_istream<charT, traits>& operator>>(
basic_streambuf<char_type, traits>* sb);
// [istream.unformatted], unformatted input
streamsize gcount() const;
int_type get();
basic_istream<charT, traits>& get(char_type& c);
basic_istream<charT, traits>& get(char_type* s, streamsize n);
basic_istream<charT, traits>& get(char_type* s, streamsize n,
char_type delim);
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb);
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb,
char_type delim);
basic_istream<charT, traits>& getline(char_type* s, streamsize n);
basic_istream<charT, traits>& getline(char_type* s, streamsize n,
char_type delim);
basic_istream<charT, traits>& ignore(
streamsize n = 1, int_type delim = traits::eof());
int_type peek();
basic_istream<charT, traits>& read (char_type* s, streamsize n);
streamsize readsome(char_type* s, streamsize n);
basic_istream<charT, traits>& putback(char_type c);
basic_istream<charT, traits>& unget();
int sync();
pos_type tellg();
basic_istream<charT, traits>& seekg(pos_type);
basic_istream<charT, traits>& seekg(off_type, ios_base::seekdir);
protected:
// [istream.cons], copy/move constructor
basic_istream(const basic_istream& rhs) = delete;
basic_istream(basic_istream&& rhs);
// [istream.assign], assign and swap
basic_istream& operator=(const basic_istream& rhs) = delete;
basic_istream& operator=(basic_istream&& rhs);
void swap(basic_istream& rhs);
};
// [istream.extractors], character extraction templates
template<class charT, class traits>
basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&,
charT&);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>&,
unsigned char&);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>&,
signed char&);
template<class charT, class traits>
basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&,
charT*);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>&,
unsigned char*);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>&,
signed char*);
}
The class template basic_istream defines a number of member function signatures that assist in reading and interpreting input from sequences controlled by a stream buffer.
Two groups of member function signatures share common properties: the formatted input functions (or extractors) and the unformatted input functions. Both groups of input functions are described as if they obtain (or extract) input characters by calling rdbuf()->sbumpc() or rdbuf()->sgetc(). They may use other public members of istream.
If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits::eof(), then the input function, except as explicitly noted otherwise, completes its actions and does setstate(eofbit), which may throw ios_base::failure ([iostate.flags]), before returning.
If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in error state. If badbit is on in exceptions(), the input function rethrows the exception without completing its actions, otherwise it does not throw anything and proceeds as if the called function had returned a failure indication.
explicit basic_istream(basic_streambuf<charT, traits>* sb);
Effects: Constructs an object of class basic_istream, assigning initial values to the base class by calling basic_ios::init(sb) ([basic.ios.cons]).
Postconditions: gcount() == 0
basic_istream(basic_istream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class, copying the gcount() from rhs, calling basic_ios<charT, traits>::move(rhs) to initialize the base class, and setting the gcount() for rhs to 0.
Effects: Destroys an object of class basic_istream.
Remarks: Does not perform any operations of rdbuf().
basic_istream& operator=(basic_istream&& rhs);
Effects: As if by swap(rhs).
Returns: *this.
void swap(basic_istream& rhs);
Effects: Calls basic_ios<charT, traits>::swap(rhs). Exchanges the values returned by gcount() and rhs.gcount().
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_istream<charT, traits>::sentry {
using traits_type = traits;
bool ok_; // exposition only
public:
explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
~sentry();
explicit operator bool() const { return ok_; }
sentry(const sentry&) = delete;
sentry& operator=(const sentry&) = delete;
};
}
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
Effects: If is.good() is false, calls is.setstate(failbit). Otherwise, prepares for formatted or unformatted input. First, if is.tie() is not a null pointer, the function calls is.tie()->flush() to synchronize the output sequence with any associated external C stream. Except that this call can be suppressed if the put area of is.tie() is empty. Further an implementation is allowed to defer the call to flush until a call of is.rdbuf()->underflow() occurs. If no such call occurs before the sentry object is destroyed, the call to flush may be eliminated entirely.308 If noskipws is zero and is.flags() & ios_base::skipws is nonzero, the function extracts and discards each character as long as the next available input character c is a whitespace character. If is.rdbuf()->sbumpc() or is.rdbuf()->sgetc() returns traits::eof(), the function calls setstate(failbit | eofbit) (which may throw ios_base::failure).
Remarks: The constructor explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false) uses the currently imbued locale in is, to determine whether the next input character is whitespace or not.
To decide if the character c is a whitespace character, the constructor performs as if it executes the following code fragment:
const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc());
if (ctype.is(ctype.space, c) != 0)
// c is a whitespace character.
If, after any preparation is completed, is.good() is true, ok_ != false otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure ([iostate.flags]))309
Effects: None.
explicit operator bool() const;
Effects: Returns ok_.
This will be possible only in functions that are part of the library. The semantics of the constructor used in user code is as specified.
Each formatted input function begins execution by constructing an object of class sentry with the noskipws (second) argument false. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. If an exception is thrown during input then ios::badbit is turned on310 in *this's error state. If (exceptions()&badbit) != 0 then the exception is rethrown. In any case, the formatted input function destroys the sentry object. If no exception has been thrown, it returns *this.
This is done without causing an ios::failure to be thrown.
operator>>(unsigned short& val);
operator>>(unsigned int& val);
operator>>(long& val);
operator>>(unsigned long& val);
operator>>(long long& val);
operator>>(unsigned long long& val);
operator>>(float& val);
operator>>(double& val);
operator>>(long double& val);
operator>>(bool& val);
operator>>(void*& val);
As in the case of the inserters, these extractors depend on the locale's num_get<> ([locale.num.get]) object to perform parsing the input stream data. These extractors behave as formatted input functions (as described in [istream.formatted.reqmts]). After a sentry object is constructed, the conversion occurs as if performed by the following code fragment:
using numget = num_get< charT, istreambuf_iterator<charT, traits>>; iostate err = iostate::goodbit; use_facet<numget >(loc).get(*this, 0, *this, err, val); setstate(err);
In the above fragment, loc stands for the private member of the basic_ios class. [ Note: The first argument provides an object of the istreambuf_iterator class which is an iterator pointed to an input stream. It bypasses istreams and uses streambufs directly. — end note ] Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream.
The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):
using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<short>::min()) {
err |= ios_base::failbit;
val = numeric_limits<short>::min();
} else if (numeric_limits<short>::max() < lval) {
err |= ios_base::failbit;
val = numeric_limits<short>::max();
} else
val = static_cast<short>(lval);
setstate(err);
The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment):
using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<int>::min()) {
err |= ios_base::failbit;
val = numeric_limits<int>::min();
} else if (numeric_limits<int>::max() < lval) {
err |= ios_base::failbit;
val = numeric_limits<int>::max();
} else
val = static_cast<int>(lval);
setstate(err);
basic_istream<charT, traits>& operator>>
(basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&));
Effects: None. This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
basic_istream<charT, traits>& operator>>
(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
Effects: Calls pf(*this). This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
Returns: *this.
basic_istream<charT, traits>& operator>>
(ios_base& (*pf)(ios_base&));
Effects: Calls pf(*this).312 This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
Returns: *this.
template<class charT, class traits>
basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in,
charT* s);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in,
unsigned char* s);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in,
signed char* s);
Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in. After a sentry object is constructed, operator>> extracts characters and stores them into successive locations of an array whose first element is designated by s. If width() is greater than zero, n is width(). Otherwise n is the number of elements of the largest array of char_type that can store a terminating charT(). n is the maximum number of characters stored.
operator>> then stores a null byte (charT()) in the next position, which may be the first position if no characters were extracted. operator>> then calls width(0).
If the function extracted no characters, it calls setstate(failbit), which may throw ios_base::failure ([iostate.flags]).
Returns: in.
template<class charT, class traits>
basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in,
charT& c);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in,
unsigned char& c);
template<class traits>
basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in,
signed char& c);
Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in. After a sentry object is constructed a character is extracted from in, if one is available, and stored in c. Otherwise, the function calls in.setstate(failbit).
Returns: in.
basic_istream<charT, traits>& operator>>
(basic_streambuf<charT, traits>* sb);
Effects: Behaves as an unformatted input function ([istream.unformatted]). If sb is null, calls setstate(failbit), which may throw ios_base::failure ([iostate.flags]). After a sentry object is constructed, extracts characters from *this and inserts them in the output sequence controlled by sb. Characters are extracted and inserted until any of the following occurs:
end-of-file occurs on the input sequence;
inserting in the output sequence fails (in which case the character to be inserted is not extracted);
an exception occurs (in which case the exception is caught).
If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure ([iostate.flags]). If it inserted no characters because it caught an exception thrown while extracting characters from *this and failbit is on in exceptions() ([iostate.flags]), then the caught exception is rethrown.
Returns: *this.
See, for example, the function signature ws(basic_istream&) ([istream.manip]).
See, for example, the function signature dec(ios_base&) ([basefield.manip]).
Each unformatted input function begins execution by constructing an object of class sentry with the default argument noskipws (second) argument true. If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input. Otherwise, if the sentry constructor exits by throwing an exception or if the sentry object returns false, when converted to a value of type bool, the function returns without attempting to obtain any input. In either case the number of extracted characters is set to 0; unformatted input functions taking a character array of nonzero size as an argument shall also store a null character (using charT()) in the first location of the array. If an exception is thrown during input then ios::badbit is turned on313 in *this's error state. (Exceptions thrown from basic_ios<>::clear() are not caught or rethrown.) If (exceptions()&badbit) != 0 then the exception is rethrown. It also counts the number of characters extracted. If no exception has been thrown it ends by storing the count in a member object and returning the value specified. In any event the sentry object is destroyed before leaving the unformatted input function.
Effects: None. This member function does not behave as an unformatted input function (as described above).
Returns: The number of characters extracted by the last unformatted input member function called for the object.
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts a character c, if one is available. Otherwise, the function calls setstate(failbit), which may throw ios_base::failure ([iostate.flags]),
Returns: c if available, otherwise traits::eof().
basic_istream<charT, traits>& get(char_type& c);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts a character, if one is available, and assigns it to c.314 Otherwise, the function calls setstate(failbit) (which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
basic_istream<charT, traits>& get(char_type* s, streamsize n,
char_type delim);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.315 Characters are extracted and stored until any of the following occurs:
n is less than one or n - 1 characters are stored;
end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));
traits::eq(c, delim) for the next available input character c (in which case c is not extracted).
If the function stores no characters, it calls setstate(failbit) (which may throw ios_base::failure ([iostate.flags])). In any case, if n is greater than zero it then stores a null character into the next successive location of the array.
Returns: *this.
basic_istream<charT, traits>& get(char_type* s, streamsize n);
Effects: Calls get(s, n, widen('\n')).
Returns: Value returned by the call.
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb,
char_type delim);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and inserts them in the output sequence controlled by sb. Characters are extracted and inserted until any of the following occurs:
end-of-file occurs on the input sequence;
inserting in the output sequence fails (in which case the character to be inserted is not extracted);
traits::eq(c, delim) for the next available input character c (in which case c is not extracted);
an exception occurs (in which case, the exception is caught but not rethrown).
If the function inserts no characters, it calls setstate(failbit), which may throw ios_base::failure ([iostate.flags]).
Returns: *this.
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb);
Effects: Calls get(sb, widen('\n')).
Returns: Value returned by the call.
basic_istream<charT, traits>& getline(char_type* s, streamsize n,
char_type delim);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and stores them into successive locations of an array whose first element is designated by s.316 Characters are extracted and stored until one of the following occurs:
end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));
traits::eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);317
n is less than one or n - 1 characters are stored (in which case the function calls setstate(failbit)).
If the function extracts no characters, it calls setstate(failbit) (which may throw ios_base::failure ([iostate.flags])).319
In any case, if n is greater than zero, it then stores a null character (using charT()) into the next successive location of the array.
Returns: *this.
[ Example:
#include <iostream>
int main() {
using namespace std;
const int line_buffer_size = 100;
char buffer[line_buffer_size];
int line_number = 0;
while (cin.getline(buffer, line_buffer_size, '\n') || cin.gcount()) {
int count = cin.gcount();
if (cin.eof())
cout << "Partial final line"; // cin.fail() is false
else if (cin.fail()) {
cout << "Partial long line";
cin.clear(cin.rdstate() & ~ios_base::failbit);
} else {
count--; // Don't include newline in count
cout << "Line " << ++line_number;
}
cout << " (" << count << " chars): " << buffer << endl;
}
}
— end example ]
basic_istream<charT, traits>& getline(char_type* s, streamsize n);
Returns: getline(s, n, widen('\n'))
basic_istream<charT, traits>&
ignore(streamsize n = 1, int_type delim = traits::eof());
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, extracts characters and discards them. Characters are extracted until any of the following occurs:
n != numeric_limits<streamsize>::max() ([limits]) and n characters have been extracted so far
end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_base::failure ([iostate.flags]));
traits::eq_int_type(traits::to_int_type(c), delim) for the next available input character c (in which case c is extracted).
Remarks: The last condition will never occur if traits::eq_int_type(delim, traits::eof()).
Returns: *this.
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, reads but does not extract the current input character.
Returns: traits::eof() if good() is false. Otherwise, returns rdbuf()->sgetc().
basic_istream<charT, traits>& read(char_type* s, streamsize n);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s.320 Characters are extracted and stored until either of the following occurs:
n characters are stored;
end-of-file occurs on the input sequence (in which case the function calls setstate(failbit | eofbit), which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
streamsize readsome(char_type* s, streamsize n);
Effects: Behaves as an unformatted input function (as described above). After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. Otherwise extracts characters and stores them into successive locations of an array whose first element is designated by s. If rdbuf()->in_avail() == -1, calls setstate(eofbit) (which may throw ios_base::failure ([iostate.flags])), and extracts no characters;
If rdbuf()->in_avail() == 0, extracts no characters
If rdbuf()->in_avail() > 0, extracts min(rdbuf()->in_avail(), n)).
Returns: The number of characters extracted.
basic_istream<charT, traits>& putback(char_type c);
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit. After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf->sputbackc(). If rdbuf() is null, or if sputbackc() returns traits::eof(), calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])). [ Note: This function extracts no characters, so the value returned by the next call to gcount() is 0. — end note ]
Returns: *this.
basic_istream<charT, traits>& unget();
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit. After constructing a sentry object, if !good() calls setstate(failbit) which may throw an exception, and return. If rdbuf() is not null, calls rdbuf()->sungetc(). If rdbuf() is null, or if sungetc() returns traits::eof(), calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])). [ Note: This function extracts no characters, so the value returned by the next call to gcount() is 0. — end note ]
Returns: *this.
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if rdbuf() is a null pointer, returns -1. Otherwise, calls rdbuf()->pubsync() and, if that function returns -1 calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags]), and returns -1. Otherwise, returns zero.
Effects: Behaves as an unformatted input function (as described above), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to gcount().
Returns: After constructing a sentry object, if fail() != false, returns pos_type(-1) to indicate failure. Otherwise, returns rdbuf()->pubseekoff(0, cur, in).
basic_istream<charT, traits>& seekg(pos_type pos);
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, it does not count the number of characters extracted, and it does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::in). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
basic_istream<charT, traits>& seekg(off_type off, ios_base::seekdir dir);
Effects: Behaves as an unformatted input function (as described above), except that the function first clears eofbit, does not count the number of characters extracted, and does not affect the value returned by subsequent calls to gcount(). After constructing a sentry object, if fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::in). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
This is done without causing an ios::failure to be thrown.
Note that this function is not overloaded on types signed char and unsigned char.
Note that this function is not overloaded on types signed char and unsigned char.
Note that this function is not overloaded on types signed char and unsigned char.
Since the final input character is “extracted,” it is counted in the gcount(), even though it is not stored.
This allows an input line which exactly fills the buffer, without setting failbit. This is different behavior than the historical AT&T implementation.
This implies an empty input line will not cause failbit to be set.
Note that this function is not overloaded on types signed char and unsigned char.
template <class charT, class traits>
basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);
Effects: Behaves as an unformatted input function ([istream.unformatted]), except that it does not count the number of characters extracted and does not affect the value returned by subsequent calls to is.gcount(). After constructing a sentry object extracts characters as long as the next available character c is whitespace or until there are no more characters in the sequence. Whitespace characters are distinguished with the same criterion as used by sentry::sentry ([istream::sentry]). If ws stops extracting characters because there are no more available it sets eofbit, but not failbit.
Returns: is.
template <class charT, class traits, class T>
basic_istream<charT, traits>&
operator>>(basic_istream<charT, traits>&& is, T&& x);
Effects: Equivalent to:
is >> std::forward<T>(x); return is;
Remarks: This function shall not participate in overload resolution unless the expression is >> std::forward<T>(x) is well-formed.
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_iostream
: public basic_istream<charT, traits>,
public basic_ostream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [iostream.cons], constructor
explicit basic_iostream(basic_streambuf<charT, traits>* sb);
// [iostream.dest], destructor
virtual ~basic_iostream();
protected:
// [iostream.cons], constructor
basic_iostream(const basic_iostream& rhs) = delete;
basic_iostream(basic_iostream&& rhs);
// [iostream.assign], assign and swap
basic_iostream& operator=(const basic_iostream& rhs) = delete;
basic_iostream& operator=(basic_iostream&& rhs);
void swap(basic_iostream& rhs);
};
}
The class template basic_iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer.
explicit basic_iostream(basic_streambuf<charT, traits>* sb);
Postconditions: rdbuf() == sb and gcount() == 0.
basic_iostream(basic_iostream&& rhs);
Effects: Move constructs from the rvalue rhs by constructing the basic_istream base class with move(rhs).
Effects: Destroys an object of class basic_iostream.
Remarks: Does not perform any operations on rdbuf().
basic_iostream& operator=(basic_iostream&& rhs);
Effects: As if by swap(rhs).
void swap(basic_iostream& rhs);
Effects: Calls basic_istream<charT, traits>::swap(rhs).
The header <ostream> defines a type and several function signatures that control output to a stream buffer along with a function template that inserts into stream rvalues.
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ostream
: virtual public basic_ios<charT, traits> {
public:
// types (inherited from basic_ios ([ios])):
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [ostream.cons], constructor/destructor
explicit basic_ostream(basic_streambuf<char_type, traits>* sb);
virtual ~basic_ostream();
// [ostream::sentry], prefix/suffix
class sentry;
// [ostream.formatted], formatted output
basic_ostream<charT, traits>& operator<<(
basic_ostream<charT, traits>& (*pf)(basic_ostream<charT, traits>&));
basic_ostream<charT, traits>& operator<<(
basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
basic_ostream<charT, traits>& operator<<(
ios_base& (*pf)(ios_base&));
basic_ostream<charT, traits>& operator<<(bool n);
basic_ostream<charT, traits>& operator<<(short n);
basic_ostream<charT, traits>& operator<<(unsigned short n);
basic_ostream<charT, traits>& operator<<(int n);
basic_ostream<charT, traits>& operator<<(unsigned int n);
basic_ostream<charT, traits>& operator<<(long n);
basic_ostream<charT, traits>& operator<<(unsigned long n);
basic_ostream<charT, traits>& operator<<(long long n);
basic_ostream<charT, traits>& operator<<(unsigned long long n);
basic_ostream<charT, traits>& operator<<(float f);
basic_ostream<charT, traits>& operator<<(double f);
basic_ostream<charT, traits>& operator<<(long double f);
basic_ostream<charT, traits>& operator<<(const void* p);
basic_ostream<charT, traits>& operator<<(nullptr_t);
basic_ostream<charT, traits>& operator<<(
basic_streambuf<char_type, traits>* sb);
// [ostream.unformatted], unformatted output
basic_ostream<charT, traits>& put(char_type c);
basic_ostream<charT, traits>& write(const char_type* s, streamsize n);
basic_ostream<charT, traits>& flush();
// [ostream.seeks], seeks
pos_type tellp();
basic_ostream<charT, traits>& seekp(pos_type);
basic_ostream<charT, traits>& seekp(off_type, ios_base::seekdir);
protected:
// [ostream.cons], copy/move constructor
basic_ostream(const basic_ostream& rhs) = delete;
basic_ostream(basic_ostream&& rhs);
// [ostream.assign], assign and swap
basic_ostream& operator=(const basic_ostream& rhs) = delete;
basic_ostream& operator=(basic_ostream&& rhs);
void swap(basic_ostream& rhs);
};
// [ostream.inserters.character], character inserters
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&,
charT);
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&,
char);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
char);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
signed char);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
unsigned char);
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&,
const charT*);
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>&,
const char*);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
const char*);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
const signed char*);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&,
const unsigned char*);
}
The class template basic_ostream defines a number of member function signatures that assist in formatting and writing output to output sequences controlled by a stream buffer.
Two groups of member function signatures share common properties: the formatted output functions (or inserters) and the unformatted output functions. Both groups of output functions generate (or insert) output characters by actions equivalent to calling rdbuf()->sputc(int_type). They may use other public members of basic_ostream except that they shall not invoke any virtual members of rdbuf() except overflow(), xsputn(), and sync().
If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in error state. If badbit is on in exceptions(), the output function rethrows the exception without completing its actions, otherwise it does not throw anything and treat as an error.
explicit basic_ostream(basic_streambuf<charT, traits>* sb);
Effects: Constructs an object of class basic_ostream, assigning initial values to the base class by calling basic_ios<charT, traits>::init(sb) ([basic.ios.cons]).
Postconditions: rdbuf() == sb.
basic_ostream(basic_ostream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by default constructing the base class and calling basic_ios<charT, traits>::move(rhs) to initialize the base class.
Effects: Destroys an object of class basic_ostream.
Remarks: Does not perform any operations on rdbuf().
basic_ostream& operator=(basic_ostream&& rhs);
Effects: As if by swap(rhs).
Returns: *this.
void swap(basic_ostream& rhs);
Effects: Calls basic_ios<charT, traits>::swap(rhs).
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ostream<charT, traits>::sentry {
bool ok_; // exposition only
public:
explicit sentry(basic_ostream<charT, traits>& os);
~sentry();
explicit operator bool() const { return ok_; }
sentry(const sentry&) = delete;
sentry& operator=(const sentry&) = delete;
};
}
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
If os.good() is nonzero, prepares for formatted or unformatted output. If os.tie() is not a null pointer, calls os.tie()->flush().321
If, after any preparation is completed, os.good() is true, ok_ == true otherwise, ok_ == false. During preparation, the constructor may call setstate(failbit) (which may throw ios_base::failure ([iostate.flags]))322
If (os.flags() & ios_base::unitbuf) && !uncaught_exceptions() && os.good() is true, calls os.rdbuf()->pubsync(). If that function returns -1, sets badbit in os.rdstate() without propagating an exception.
explicit operator bool() const;
Effects: Returns ok_.
The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.
The sentry constructor and destructor can also perform additional implementation-dependent operations.
Each seek member function begins execution by constructing an object of class sentry. It returns by destroying the sentry object.
Returns: If fail() != false, returns pos_type(-1) to indicate failure. Otherwise, returns rdbuf()->pubseekoff(0, cur, out).
basic_ostream<charT, traits>& seekp(pos_type pos);
Effects: If fail() != true, executes rdbuf()->pubseekpos(pos, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
basic_ostream<charT, traits>& seekp(off_type off, ios_base::seekdir dir);
Effects: If fail() != true, executes rdbuf()->pubseekoff(off, dir, ios_base::out). In case of failure, the function calls setstate(failbit) (which may throw ios_base::failure).
Returns: *this.
Each formatted output function begins execution by constructing an object of class sentry. If this object returns true when converted to a value of type bool, the function endeavors to generate the requested output. If the generation fails, then the formatted output function does setstate(ios_base::failbit), which might throw an exception. If an exception is thrown during output, then ios::badbit is turned on323 in *this's error state. If (exceptions()&badbit) != 0 then the exception is rethrown. Whether or not an exception is thrown, the sentry object is destroyed before leaving the formatted output function. If no exception is thrown, the result of the formatted output function is *this.
The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.
If a formatted output function of a stream os determines padding, it does so as follows. Given a charT character sequence seq where charT is the character type of the stream, if the length of seq is less than os.width(), then enough copies of os.fill() are added to this sequence as necessary to pad to a width of os.width() characters. If (os.flags() & ios_base::adjustfield) == ios_base::left is true, the fill characters are placed after the character sequence; otherwise, they are placed before the character sequence.
without causing an ios::failure to be thrown.
operator<<(bool val);
operator<<(short val);
operator<<(unsigned short val);
operator<<(int val);
operator<<(unsigned int val);
operator<<(long val);
operator<<(unsigned long val);
operator<<(long long val);
operator<<(unsigned long long val);
operator<<(float val);
operator<<(double val);
operator<<(long double val);
operator<<(const void* val);
Effects: The classes num_get<> and num_put<> handle locale-dependent numeric formatting and parsing. These inserter functions use the imbued locale value to perform numeric formatting. When val is of type bool, long, unsigned long, long long, unsigned long long, double, long double, or const void*, the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT, ostreambuf_iterator<charT, traits>>
>(getloc()).put(*this, *this, fill(), val).failed();
When val is of type short the formatting conversion occurs as if it performed the following code fragment:
ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
num_put<charT, ostreambuf_iterator<charT, traits>>
>(getloc()).put(*this, *this, fill(),
baseflags == ios_base::oct || baseflags == ios_base::hex
? static_cast<long>(static_cast<unsigned short>(val))
: static_cast<long>(val)).failed();
When val is of type int the formatting conversion occurs as if it performed the following code fragment:
ios_base::fmtflags baseflags = ios_base::flags() & ios_base::basefield;
bool failed = use_facet<
num_put<charT, ostreambuf_iterator<charT, traits>>
>(getloc()).put(*this, *this, fill(),
baseflags == ios_base::oct || baseflags == ios_base::hex
? static_cast<long>(static_cast<unsigned int>(val))
: static_cast<long>(val)).failed();
When val is of type unsigned short or unsigned int the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT, ostreambuf_iterator<charT, traits>>
>(getloc()).put(*this, *this, fill(),
static_cast<unsigned long>(val)).failed();
When val is of type float the formatting conversion occurs as if it performed the following code fragment:
bool failed = use_facet<
num_put<charT, ostreambuf_iterator<charT, traits>>
>(getloc()).put(*this, *this, fill(),
static_cast<double>(val)).failed();
The first argument provides an object of the ostreambuf_iterator<> class which is an iterator for class basic_ostream<>. It bypasses ostreams and uses streambufs directly. Class locale relies on these types as its interface to iostreams, since for flexibility it has been abstracted away from direct dependence on ostream. The second parameter is a reference to the base subobject of type ios_base. It provides formatting specifications such as field width, and a locale from which to obtain other facets. If failed is true then does setstate(badbit), which may throw an exception, and returns.
Returns: *this.
basic_ostream<charT, traits>& operator<<
(basic_ostream<charT, traits>& (*pf)(basic_ostream<charT, traits>&));
Effects: None. Does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
basic_ostream<charT, traits>& operator<<
(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
basic_ostream<charT, traits>& operator<<
(ios_base& (*pf)(ios_base&));
Effects: Calls pf(*this). This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
Returns: *this.
basic_ostream<charT, traits>& operator<<
(basic_streambuf<charT, traits>* sb);
Effects: Behaves as an unformatted output function ([ostream.unformatted]). After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_base::failure).
Gets characters from sb and inserts them in *this. Characters are read from sb and inserted until any of the following occurs:
end-of-file occurs on the input sequence;
inserting in the output sequence fails (in which case the character to be inserted is not extracted);
an exception occurs while getting a character from sb.
If the function inserts no characters, it calls setstate(failbit) (which may throw ios_base::failure ([iostate.flags])). If an exception was thrown while extracting a character, the function sets failbit in error state, and if failbit is on in exceptions() the caught exception is rethrown.
Returns: *this.
basic_ostream<charT, traits>& operator<<(nullptr_t);
Effects: Equivalent to:
return *this << s;
where s is an implementation-defined NTCTS ([defns.ntcts]).
See, for example, the function signature endl(basic_ostream&) ([ostream.manip]).
See, for example, the function signature dec(ios_base&) ([basefield.manip]).
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out,
charT c);
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out,
char c);
// specialization
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
char c);
// signed and unsigned
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
signed char c);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
unsigned char c);
Effects: Behaves as a formatted output function ( [ostream.formatted.reqmts]) of out. Constructs a character sequence seq. If c has type char and the character type of the stream is not char, then seq consists of out.widen(c); otherwise seq consists of c. Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls os.width(0).
Returns: out.
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out,
const charT* s);
template<class charT, class traits>
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& out,
const char* s);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
const char* s);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
const signed char* s);
template<class traits>
basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>& out,
const unsigned char* s);
Requires: s shall not be a null pointer.
Effects: Behaves like a formatted inserter (as described in [ostream.formatted.reqmts]) of out. Creates a character sequence seq of n characters starting at s, each widened using out.widen() ([basic.ios.members]), where n is the number that would be computed as if by:
traits::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const charT*, and also for the overload where the first argument is of type basic_ostream<char, traits>& and the second is of type const char*,
char_traits<char>::length(s) for the overload where the first argument is of type basic_ostream<charT, traits>& and the second is of type const char*,
traits::length(reinterpret_cast<const char*>(s)) for the other two overloads.
Determines padding for seq as described in [ostream.formatted.reqmts]. Inserts seq into out. Calls width(0).
Returns: out.
Each unformatted output function begins execution by constructing an object of class sentry. If this object returns true, while converting to a value of type bool, the function endeavors to generate the requested output. If an exception is thrown during output, then ios::badbit is turned on326 in *this's error state. If (exceptions() & badbit) != 0 then the exception is rethrown. In any case, the unformatted output function ends by destroying the sentry object, then, if no exception was thrown, returning the value specified for the unformatted output function.
Effects: Behaves as an unformatted output function (as described above). After constructing a sentry object, inserts the character c, if possible.327
Otherwise, calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
basic_ostream& write(const char_type* s, streamsize n);
Effects: Behaves as an unformatted output function (as described above). After constructing a sentry object, obtains characters to insert from successive locations of an array whose first element is designated by s.328 Characters are inserted until either of the following occurs:
n characters are inserted;
inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_base::failure ([iostate.flags])).
Returns: *this.
Effects: Behaves as an unformatted output function (as described above). If rdbuf() is not a null pointer, constructs a sentry object. If this object returns true when converted to a value of type bool the function calls rdbuf()->pubsync(). If that function returns -1 calls setstate(badbit) (which may throw ios_base::failure ([iostate.flags])). Otherwise, if the sentry object returns false, does nothing.
Returns: *this.
without causing an ios::failure to be thrown.
Note that this function is not overloaded on types signed char and unsigned char.
Note that this function is not overloaded on types signed char and unsigned char.
template <class charT, class traits>
basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
Effects: Calls os.put(os.widen('\n')), then os.flush().
Returns: os.
template <class charT, class traits>
basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
Effects: Inserts a null character into the output sequence: calls os.put(charT()).
Returns: os.
template <class charT, class traits>
basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);
Effects: Calls os.flush().
Returns: os.
template <class charT, class traits, class T>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>&& os, const T& x);
Effects: As if by: os << x;
Returns: os
Remarks: This function shall not participate in overload resolution unless the expression os << x is well-formed.
The header <iomanip> defines several functions that support extractors and inserters that alter information maintained by class ios_base and its derived classes.
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << resetiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> resetiosflags(mask) behaves as if it called f(in, mask), where the function f is defined as:329
void f(ios_base& str, ios_base::fmtflags mask) {
// reset specified flags
str.setf(ios_base::fmtflags(0), mask);
}
The expression out << resetiosflags(mask) shall have type basic_ostream<charT, traits>& and value out. The expression in >> resetiosflags(mask) shall have type basic_istream<charT, traits>& and value in.
unspecified setiosflags(ios_base::fmtflags mask);
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setiosflags(mask) behaves as if it called f(out, mask), or if in is an object of type basic_istream<charT, traits> then the expression in >> setiosflags(mask) behaves as if it called f(in, mask), where the function f is defined as:
void f(ios_base& str, ios_base::fmtflags mask) {
// set specified flags
str.setf(mask);
}
The expression
out << setiosflags(mask)
shall have type
basic_ostream<charT, traits>&
and value
out.
The expression
in >> setiosflags(mask)
shall have type
basic_istream<charT,
traits>&
and value
in.
unspecified setbase(int base);
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setbase(base) behaves as if it called f(out, base), or if in is an object of type basic_istream<charT, traits> then the expression in >> setbase(base) behaves as if it called f(in, base), where the function f is defined as:
void f(ios_base& str, int base) {
// set basefield
str.setf(base == 8 ? ios_base::oct :
base == 10 ? ios_base::dec :
base == 16 ? ios_base::hex :
ios_base::fmtflags(0), ios_base::basefield);
}
The expression out << setbase(base) shall have type basic_ostream<charT, traits>& and value out. The expression in >> setbase(base) shall have type basic_istream<charT, traits>& and value in.
unspecified setfill(char_type c);
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> and c has type charT then the expression out << setfill(c) behaves as if it called f(out, c), where the function f is defined as:
template<class charT, class traits>
void f(basic_ios<charT, traits>& str, charT c) {
// set fill character
str.fill(c);
}
The expression out << setfill(c) shall have type basic_ostream<charT, traits>& and value out.
unspecified setprecision(int n);
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << setprecision(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setprecision(n) behaves as if it called f(in, n), where the function f is defined as:
void f(ios_base& str, int n) {
// set precision
str.precision(n);
}
The expression out << setprecision(n) shall have type basic_ostream<charT, traits>& and value out. The expression in >> setprecision(n) shall have type basic_istream<charT, traits>& and value in.
Returns: An object of unspecified type such that if out is an instance of basic_ostream<charT, traits> then the expression out << setw(n) behaves as if it called f(out, n), or if in is an object of type basic_istream<charT, traits> then the expression in >> setw(n) behaves as if it called f(in, n), where the function f is defined as:
void f(ios_base& str, int n) {
// set width
str.width(n);
}
The expression out << setw(n) shall have type basic_ostream<charT, traits>& and value out. The expression in >> setw(n) shall have type basic_istream<charT, traits>& and value in.
The expression cin >> resetiosflags(ios_base::skipws) clears ios_base::skipws in the format flags stored in the basic_istream<charT, traits> object cin (the same as cin >> noskipws), and the expression cout << resetiosflags(ios_base::showbase) clears ios_base::showbase in the format flags stored in the basic_ostream<charT, traits> object cout (the same as cout << noshowbase).
The header <iomanip> defines several functions that support extractors and inserters that allow for the parsing and formatting of sequences and values for money and time.
template <class moneyT> unspecified get_money(moneyT& mon, bool intl = false);
Requires: The type moneyT shall be either long double or a specialization of the basic_string template (Clause [strings]).
Effects: The expression in >> get_money(mon, intl) described below behaves as a formatted input function ([istream.formatted.reqmts]).
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_money(mon, intl) behaves as if it called f(in, mon, intl), where the function f is defined as:
template <class charT, class traits, class moneyT>
void f(basic_ios<charT, traits>& str, moneyT& mon, bool intl) {
using Iter = istreambuf_iterator<charT, traits>;
using MoneyGet = money_get<charT, Iter>;
ios_base::iostate err = ios_base::goodbit;
const MoneyGet &mg = use_facet<MoneyGet>(str.getloc());
mg.get(Iter(str.rdbuf()), Iter(), intl, str, err, mon);
if (ios_base::goodbit != err)
str.setstate(err);
}
The expression in >> get_money(mon, intl) shall have type basic_istream<charT, traits>& and value in.
template <class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);
Requires: The type moneyT shall be either long double or a specialization of the basic_string template (Clause [strings]).
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_money(mon, intl) behaves as a formatted output function ([ostream.formatted.reqmts]) that calls f(out, mon, intl), where the function f is defined as:
template <class charT, class traits, class moneyT>
void f(basic_ios<charT, traits>& str, const moneyT& mon, bool intl) {
using Iter = ostreambuf_iterator<charT, traits>;
using MoneyPut = money_put<charT, Iter>;
const MoneyPut& mp = use_facet<MoneyPut>(str.getloc());
const Iter end = mp.put(Iter(str.rdbuf()), intl, str, str.fill(), mon);
if (end.failed())
str.setstate(ios::badbit);
}
The expression out << put_money(mon, intl) shall have type basic_ostream<charT, traits>& and value out.
template <class charT> unspecified get_time(struct tm* tmb, const charT* fmt);
Requires: The argument tmb shall be a valid pointer to an object of type struct tm, and the argument fmt shall be a valid pointer to an array of objects of type charT with char_traits<charT>::length(fmt) elements.
Returns: An object of unspecified type such that if in is an object of type basic_istream<charT, traits> then the expression in >> get_time(tmb, fmt) behaves as if it called f(in, tmb, fmt), where the function f is defined as:
template <class charT, class traits>
void f(basic_ios<charT, traits>& str, struct tm* tmb, const charT* fmt) {
using Iter = istreambuf_iterator<charT, traits>;
using TimeGet = time_get<charT, Iter>;
ios_base::iostate err = ios_base::goodbit;
const TimeGet& tg = use_facet<TimeGet>(str.getloc());
tg.get(Iter(str.rdbuf()), Iter(), str, err, tmb,
fmt, fmt + traits::length(fmt));
if (err != ios_base::goodbit)
str.setstate(err);
}
The expression in >> get_time(tmb, fmt) shall have type basic_istream<charT, traits>& and value in.
template <class charT> unspecified put_time(const struct tm* tmb, const charT* fmt);
Requires: The argument tmb shall be a valid pointer to an object of type struct tm, and the argument fmt shall be a valid pointer to an array of objects of type charT with char_traits<charT>::length(fmt) elements.
Returns: An object of unspecified type such that if out is an object of type basic_ostream<charT, traits> then the expression out << put_time(tmb, fmt) behaves as if it called f(out, tmb, fmt), where the function f is defined as:
template <class charT, class traits>
void f(basic_ios<charT, traits>& str, const struct tm* tmb, const charT* fmt) {
using Iter = ostreambuf_iterator<charT, traits>;
using TimePut = time_put<charT, Iter>;
const TimePut& tp = use_facet<TimePut>(str.getloc());
const Iter end = tp.put(Iter(str.rdbuf()), str, str.fill(), tmb,
fmt, fmt + traits::length(fmt));
if (end.failed())
str.setstate(ios_base::badbit);
}
The expression out << put_time(tmb, fmt) shall have type basic_ostream<charT, traits>& and value out.
[ Note: Quoted manipulators provide string insertion and extraction of quoted strings (for example, XML and CSV formats). Quoted manipulators are useful in ensuring that the content of a string with embedded spaces remains unchanged if inserted and then extracted via stream I/O. — end note ]
template <class charT>
unspecified quoted(const charT* s, charT delim = charT('"'), charT escape = charT('\\'));
template <class charT, class traits, class Allocator>
unspecified quoted(const basic_string<charT, traits, Allocator>& s,
charT delim = charT('"'), charT escape = charT('\\'));
Returns: An object of unspecified type such that if out is an instance of basic_ostream with member type char_type the same as charT and with member type traits_type, which in the second form is the same as traits, then the expression out << quoted(s, delim, escape) behaves as a formatted output function ([ostream.formatted.reqmts]) of out. This forms a character sequence seq, initially consisting of the following elements:
delim.
Each character in s. If the character to be output is equal to escape or delim, as determined by traits_type::eq, first output escape.
delim.
Let x be the number of elements initially in seq. Then padding is determined for seq as described in [ostream.formatted.reqmts], seq is inserted as if by calling out.rdbuf()->sputn(seq, n), where n is the larger of out.width() and x, and out.width(0) is called. The expression out << quoted(s, delim, escape) shall have type basic_ostream<charT, traits>& and value out.
template <class charT, class traits, class Allocator>
unspecified quoted(basic_string<charT, traits, Allocator>& s,
charT delim = charT('"'), charT escape = charT('\\'));
Returns: An object of unspecified type such that:
If in is an instance of basic_istream with member types char_type and traits_type the same as charT and traits, respectively, then the expression in >> quoted(s, delim, escape) behaves as if it extracts the following characters from in using operator>>(basic_istream<charT, traits>&, charT&) ([istream.extractors]) which may throw ios_base::failure ([ios::failure]):
If the first character extracted is equal to delim, as determined by traits_type::eq, then:
Turn off the skipws flag.
s.clear()
Until an unescaped delim character is reached or !in, extract characters from in and append them to s, except that if an escape is reached, ignore it and append the next character to s.
Discard the final delim character.
Restore the skipws flag to its original value.
Otherwise, in >> s.
If out is an instance of basic_ostream with member types char_type and traits_type the same as charT and traits, respectively, then the expression out << quoted(s, delim, escape) behaves as specified for the const basic_string<charT, traits, Allocator>& overload of the quoted function.
The expression in >> quoted(s, delim, escape) shall have type basic_istream<charT, traits>& and value in. The expression out << quoted(s, delim, escape) shall have type basic_ostream<charT, traits>& and value out.
The header <sstream> defines four class templates and eight types that associate stream buffers with objects of class basic_string, as described in [string.classes].
namespace std {
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringbuf;
using stringbuf = basic_stringbuf<char>;
using wstringbuf = basic_stringbuf<wchar_t>;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_istringstream;
using istringstream = basic_istringstream<char>;
using wistringstream = basic_istringstream<wchar_t>;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_ostringstream;
using ostringstream = basic_ostringstream<char>;
using wostringstream = basic_ostringstream<wchar_t>;
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringstream;
using stringstream = basic_stringstream<char>;
using wstringstream = basic_stringstream<wchar_t>;
}
namespace std {
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringbuf
: public basic_streambuf<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
using allocator_type = Allocator;
// [stringbuf.cons], constructors
explicit basic_stringbuf(
ios_base::openmode which = ios_base::in | ios_base::out);
explicit basic_stringbuf(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::in | ios_base::out);
basic_stringbuf(const basic_stringbuf& rhs) = delete;
basic_stringbuf(basic_stringbuf&& rhs);
// [stringbuf.assign], assign and swap
basic_stringbuf& operator=(const basic_stringbuf& rhs) = delete;
basic_stringbuf& operator=(basic_stringbuf&& rhs);
void swap(basic_stringbuf& rhs);
// [stringbuf.members], get and set
basic_string<charT, traits, Allocator> str() const;
void str(const basic_string<charT, traits, Allocator>& s);
protected:
// [stringbuf.virtuals], overridden virtual functions
int_type underflow() override;
int_type pbackfail(int_type c = traits::eof()) override;
int_type overflow (int_type c = traits::eof()) override;
basic_streambuf<charT, traits>* setbuf(charT*, streamsize) override;
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
private:
ios_base::openmode mode; // exposition only
};
template <class charT, class traits, class Allocator>
void swap(basic_stringbuf<charT, traits, Allocator>& x,
basic_stringbuf<charT, traits, Allocator>& y);
}
The class basic_stringbuf is derived from basic_streambuf to associate possibly the input sequence and possibly the output sequence with a sequence of arbitrary characters. The sequence can be initialized from, or made available as, an object of class basic_string.
For the sake of exposition, the maintained data is presented here as:
ios_base::openmode mode, has in set if the input sequence can be read, and out set if the output sequence can be written.
explicit basic_stringbuf(
ios_base::openmode which = ios_base::in | ios_base::out);
Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() ([streambuf.cons]), and initializing mode with which.
Postconditions: str() == "".
explicit basic_stringbuf(
const basic_string<charT, traits, Allocator>& s,
ios_base::openmode which = ios_base::in | ios_base::out);
Effects: Constructs an object of class basic_stringbuf, initializing the base class with basic_streambuf() ([streambuf.cons]), and initializing mode with which. Then calls str(s).
basic_stringbuf(basic_stringbuf&& rhs);
Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. The openmode, locale and any other state of rhs is also copied.
Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.
str() == rhs_p.str()
gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
if (eback()) eback() != rhs_a.eback()
if (gptr()) gptr() != rhs_a.gptr()
if (egptr()) egptr() != rhs_a.egptr()
if (pbase()) pbase() != rhs_a.pbase()
if (pptr()) pptr() != rhs_a.pptr()
if (epptr()) epptr() != rhs_a.epptr()
basic_stringbuf& operator=(basic_stringbuf&& rhs);
Effects: After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [stringbuf.cons]).
Returns: *this.
void swap(basic_stringbuf& rhs);
Effects: Exchanges the state of *this and rhs.
template <class charT, class traits, class Allocator>
void swap(basic_stringbuf<charT, traits, Allocator>& x,
basic_stringbuf<charT, traits, Allocator>& y);
Effects: As if by x.swap(y).
basic_string<charT, traits, Allocator> str() const;
Returns: A basic_string object whose content is equal to the basic_stringbuf underlying character sequence. If the basic_stringbuf was created only in input mode, the resultant basic_string contains the character sequence in the range [eback(), egptr()). If the basic_stringbuf was created with which & ios_base::out being nonzero then the resultant basic_string contains the character sequence in the range [pbase(), high_mark), where high_mark represents the position one past the highest initialized character in the buffer. Characters can be initialized by writing to the stream, by constructing the basic_stringbuf with a basic_string, or by calling the str(basic_string) member function. In the case of calling the str(basic_string) member function, all characters initialized prior to the call are now considered uninitialized (except for those characters re-initialized by the new basic_string). Otherwise the basic_stringbuf has been created in neither input nor output mode and a zero length basic_string is returned.
void str(const basic_string<charT, traits, Allocator>& s);
Effects: Copies the content of s into the basic_stringbuf underlying character sequence and initializes the input and output sequences according to mode.
Postconditions: If mode & ios_base::out is nonzero, pbase() points to the first underlying character and epptr() >= pbase() + s.size() holds; in addition, if mode & ios_base::ate is nonzero, pptr() == pbase() + s.size() holds, otherwise pptr() == pbase() is true. If mode & ios_base::in is nonzero, eback() points to the first underlying character, and both gptr() == eback() and egptr() == eback() + s.size() hold.
int_type underflow() override;
Returns: If the input sequence has a read position available, returns traits::to_int_type(*gptr()). Otherwise, returns traits::eof(). Any character in the underlying buffer which has been initialized is considered to be part of the input sequence.
int_type pbackfail(int_type c = traits::eof()) override;
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
If traits::eq_int_type(c, traits::eof()) returns false and if the input sequence has a putback position available, and if traits::eq(to_char_type(c), gptr()[-1]) returns true, assigns gptr() - 1 to gptr().
Returns: c.
If traits::eq_int_type(c, traits::eof()) returns false and if the input sequence has a putback position available, and if mode & ios_base::out is nonzero, assigns c to *-- gptr().
Returns: c.
If traits::eq_int_type(c, traits::eof()) returns true and if the input sequence has a putback position available, assigns gptr() - 1 to gptr().
Returns: traits::not_eof(c).
Returns: traits::eof() to indicate failure.
int_type overflow(int_type c = traits::eof()) override;
Effects: Appends the character designated by c to the output sequence, if possible, in one of two ways:
If traits::eq_int_type(c, traits::eof()) returns false and if either the output sequence has a write position available or the function makes a write position available (as described below), the function calls sputc(c).
Signals success by returning c.
If traits::eq_int_type(c, traits::eof()) returns true, there is no character to append.
Signals success by returning a value other than traits::eof().
Remarks: The function can alter the number of write positions available as a result of any call.
Returns: traits::eof() to indicate failure.
The function can make a write position available only if (mode & ios_base::out) != 0. To make a write position available, the function reallocates (or initially allocates) an array object with a sufficient number of elements to hold the current array object (if any), plus at least one additional write position. If (mode & ios_base::in) != 0, the function alters the read end pointer egptr() to point just past the new write position.
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
Effects: Alters the stream position within one of the controlled sequences, if possible, as indicated in Table [tab:iostreams.seekoff.positioning].
| Conditions | Result |
| (which & ios_base::in) == ios_base::in | positions the input sequence |
| (which & ios_base::out) == ios_base::out | positions the output sequence |
|
(which & (ios_base::in | ios_base::out)) == (ios_base::in) | ios_base::out)) and way == either ios_base::beg or ios_base::end | positions both the input and the output sequences |
| Otherwise | the positioning operation fails. |
For a sequence to be positioned, if its next pointer (either gptr() or pptr()) is a null pointer and the new offset newoff is nonzero, the positioning operation fails. Otherwise, the function determines newoff as indicated in Table [tab:iostreams.newoff.values].
| Condition | newoff Value |
| way == ios_base::beg | 0 |
| way == ios_base::cur | the next pointer minus the beginning pointer (xnext - xbeg). |
| way == ios_base::end | the high mark pointer minus the beginning pointer (high_mark - xbeg). |
If (newoff + off) < 0, or if newoff + off refers to an uninitialized character ([stringbuf.members]), the positioning operation fails. Otherwise, the function assigns xbeg + newoff + off to the next pointer xnext.
Returns: pos_type(newoff), constructed from the resultant offset newoff (of type off_type), that stores the resultant stream position, if possible. If the positioning operation fails, or if the constructed object cannot represent the resultant stream position, the return value is pos_type(off_type(-1)).
pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
Effects: Equivalent to seekoff(off_type(sp), ios_base::beg, which).
Returns: sp to indicate success, or pos_type(off_type(-1)) to indicate failure.
basic_streambuf<charT, traits>* setbuf(charT* s, streamsize n);
Returns: this.
namespace std {
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_istringstream
: public basic_istream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
using allocator_type = Allocator;
// [istringstream.cons], constructors
explicit basic_istringstream(
ios_base::openmode which = ios_base::in);
explicit basic_istringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::in);
basic_istringstream(const basic_istringstream& rhs) = delete;
basic_istringstream(basic_istringstream&& rhs);
// [istringstream.assign], assign and swap
basic_istringstream& operator=(const basic_istringstream& rhs) = delete;
basic_istringstream& operator=(basic_istringstream&& rhs);
void swap(basic_istringstream& rhs);
// [istringstream.members], members
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
basic_string<charT, traits, Allocator> str() const;
void str(const basic_string<charT, traits, Allocator>& s);
private:
basic_stringbuf<charT, traits, Allocator> sb; // exposition only
};
template <class charT, class traits, class Allocator>
void swap(basic_istringstream<charT, traits, Allocator>& x,
basic_istringstream<charT, traits, Allocator>& y);
}
The class basic_istringstream<charT, traits, Allocator> supports reading objects of class basic_string<charT, traits, Allocator>. It uses a basic_stringbuf<charT, traits, Allocator> object to control the associated storage. For the sake of exposition, the maintained data is presented here as:
sb, the stringbuf object.
explicit basic_istringstream(ios_base::openmode which = ios_base::in);
Effects: Constructs an object of class basic_istringstream<charT, traits>, initializing the base class with basic_istream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::in)) ([stringbuf.cons]).
explicit basic_istringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::in);
Effects: Constructs an object of class basic_istringstream<charT, traits>, initializing the base class with basic_istream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(str, which | ios_base::in)) ([stringbuf.cons]).
basic_istringstream(basic_istringstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_stringbuf. Next basic_istream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_stringbuf.
basic_istringstream& operator=(basic_istringstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_istringstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_istream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits, class Allocator>
void swap(basic_istringstream<charT, traits, Allocator>& x,
basic_istringstream<charT, traits, Allocator>& y);
Effects: As if by x.swap(y).
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(&sb).
basic_string<charT, traits, Allocator> str() const;
Returns: rdbuf()->str().
void str(const basic_string<charT, traits, Allocator>& s);
Effects: Calls rdbuf()->str(s).
namespace std {
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_ostringstream
: public basic_ostream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
using allocator_type = Allocator;
// [ostringstream.cons], constructors
explicit basic_ostringstream(
ios_base::openmode which = ios_base::out);
explicit basic_ostringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::out);
basic_ostringstream(const basic_ostringstream& rhs) = delete;
basic_ostringstream(basic_ostringstream&& rhs);
// [ostringstream.assign], assign and swap
basic_ostringstream& operator=(const basic_ostringstream& rhs) = delete;
basic_ostringstream& operator=(basic_ostringstream&& rhs);
void swap(basic_ostringstream& rhs);
// [ostringstream.members], members
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
basic_string<charT, traits, Allocator> str() const;
void str(const basic_string<charT, traits, Allocator>& s);
private:
basic_stringbuf<charT, traits, Allocator> sb; // exposition only
};
template <class charT, class traits, class Allocator>
void swap(basic_ostringstream<charT, traits, Allocator>& x,
basic_ostringstream<charT, traits, Allocator>& y);
}
The class basic_ostringstream<charT, traits, Allocator> supports writing objects of class basic_string<charT, traits, Allocator>. It uses a basic_stringbuf object to control the associated storage. For the sake of exposition, the maintained data is presented here as:
sb, the stringbuf object.
explicit basic_ostringstream(
ios_base::openmode which = ios_base::out);
Effects: Constructs an object of class basic_ostringstream, initializing the base class with basic_ostream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(which | ios_base::out)) ([stringbuf.cons]).
explicit basic_ostringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::out);
Effects: Constructs an object of class basic_ostringstream<charT, traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(str, which | ios_base::out)) ([stringbuf.cons]).
basic_ostringstream(basic_ostringstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_stringbuf. Next basic_ostream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_stringbuf.
basic_ostringstream& operator=(basic_ostringstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_ostringstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_ostream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits, class Allocator>
void swap(basic_ostringstream<charT, traits, Allocator>& x,
basic_ostringstream<charT, traits, Allocator>& y);
Effects: As if by x.swap(y).
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(&sb).
basic_string<charT, traits, Allocator> str() const;
Returns: rdbuf()->str().
void str(const basic_string<charT, traits, Allocator>& s);
Effects: Calls rdbuf()->str(s).
namespace std {
template <class charT, class traits = char_traits<charT>,
class Allocator = allocator<charT>>
class basic_stringstream
: public basic_iostream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
using allocator_type = Allocator;
// [stringstream.cons], constructors
explicit basic_stringstream(
ios_base::openmode which = ios_base::out | ios_base::in);
explicit basic_stringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::out | ios_base::in);
basic_stringstream(const basic_stringstream& rhs) = delete;
basic_stringstream(basic_stringstream&& rhs);
// [stringstream.assign], assign and swap
basic_stringstream& operator=(const basic_stringstream& rhs) = delete;
basic_stringstream& operator=(basic_stringstream&& rhs);
void swap(basic_stringstream& rhs);
// [stringstream.members], members
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
basic_string<charT, traits, Allocator> str() const;
void str(const basic_string<charT, traits, Allocator>& str);
private:
basic_stringbuf<charT, traits> sb; // exposition only
};
template <class charT, class traits, class Allocator>
void swap(basic_stringstream<charT, traits, Allocator>& x,
basic_stringstream<charT, traits, Allocator>& y);
}
The class template basic_stringstream<charT, traits> supports reading and writing from objects of class basic_string<charT, traits, Allocator>. It uses a basic_stringbuf<charT, traits, Allocator> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as
sb, the stringbuf object.
explicit basic_stringstream(
ios_base::openmode which = ios_base::out | ios_base::in);
Effects: Constructs an object of class basic_stringstream<charT, traits>, initializing the base class with basic_iostream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(which).
explicit basic_stringstream(
const basic_string<charT, traits, Allocator>& str,
ios_base::openmode which = ios_base::out | ios_base::in);
Effects: Constructs an object of class basic_stringstream<charT, traits>, initializing the base class with basic_iostream(&sb) and initializing sb with basic_stringbuf<charT, traits, Allocator>(str, which).
basic_stringstream(basic_stringstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_stringbuf. Next basic_istream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_stringbuf.
basic_stringstream& operator=(basic_stringstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_stringstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_iostream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits, class Allocator>
void swap(basic_stringstream<charT, traits, Allocator>& x,
basic_stringstream<charT, traits, Allocator>& y);
Effects: As if by x.swap(y).
basic_stringbuf<charT, traits, Allocator>* rdbuf() const;
Returns: const_cast<basic_stringbuf<charT, traits, Allocator>*>(&sb)
basic_string<charT, traits, Allocator> str() const;
Returns: rdbuf()->str().
void str(const basic_string<charT, traits, Allocator>& str);
Effects: Calls rdbuf()->str(str).
The header <fstream> defines four class templates and eight types that associate stream buffers with files and assist reading and writing files.
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_filebuf;
using filebuf = basic_filebuf<char>;
using wfilebuf = basic_filebuf<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_ifstream;
using ifstream = basic_ifstream<char>;
using wifstream = basic_ifstream<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_ofstream;
using ofstream = basic_ofstream<char>;
using wofstream = basic_ofstream<wchar_t>;
template <class charT, class traits = char_traits<charT>>
class basic_fstream;
using fstream = basic_fstream<char>;
using wfstream = basic_fstream<wchar_t>;
}
[ Note: The class template basic_filebuf treats a file as a source or sink of bytes. In an environment that uses a large character set, the file typically holds multibyte character sequences and the basic_filebuf object converts those multibyte sequences into wide character sequences. — end note ]
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_filebuf
: public basic_streambuf<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [filebuf.cons], constructors/destructor
basic_filebuf();
basic_filebuf(const basic_filebuf& rhs) = delete;
basic_filebuf(basic_filebuf&& rhs);
virtual ~basic_filebuf();
// [filebuf.assign], assign and swap
basic_filebuf& operator=(const basic_filebuf& rhs) = delete;
basic_filebuf& operator=(basic_filebuf&& rhs);
void swap(basic_filebuf& rhs);
// [filebuf.members], members
bool is_open() const;
basic_filebuf<charT, traits>* open(const char* s,
ios_base::openmode mode);
basic_filebuf<charT, traits>* open(const string& s,
ios_base::openmode mode);
basic_filebuf<charT, traits>* close();
protected:
// [filebuf.virtuals], overridden virtual functions
streamsize showmanyc() override;
int_type underflow() override;
int_type uflow() override;
int_type pbackfail(int_type c = traits::eof()) override;
int_type overflow (int_type c = traits::eof()) override;
basic_streambuf<charT, traits>* setbuf(char_type* s,
streamsize n) override;
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
int sync() override;
void imbue(const locale& loc) override;
};
template <class charT, class traits>
void swap(basic_filebuf<charT, traits>& x,
basic_filebuf<charT, traits>& y);
}
The class basic_filebuf<charT, traits> associates both the input sequence and the output sequence with a file.
The restrictions on reading and writing a sequence controlled by an object of class basic_filebuf<charT, traits> are the same as for reading and writing with the C standard library FILEs.
In particular:
If the file is not open for reading the input sequence cannot be read.
If the file is not open for writing the output sequence cannot be written.
A joint file position is maintained for both the input sequence and the output sequence.
An instance of basic_filebuf behaves as described in [filebuf] provided traits::pos_type is fpos<traits::state_type>. Otherwise the behavior is undefined.
In order to support file I/O and multibyte/wide character conversion, conversions are performed using members of a facet, referred to as a_codecvt in following sections, obtained as if by
const codecvt<charT, char, typename traits::state_type>& a_codecvt = use_facet<codecvt<charT, char, typename traits::state_type>>(getloc());
Effects: Constructs an object of class basic_filebuf<charT, traits>, initializing the base class with basic_streambuf<charT, traits>() ([streambuf.cons]).
Postconditions: is_open() == false.
basic_filebuf(basic_filebuf&& rhs);
Effects: Move constructs from the rvalue rhs. It is implementation-defined whether the sequence pointers in *this (eback(), gptr(), egptr(), pbase(), pptr(), epptr()) obtain the values which rhs had. Whether they do or not, *this and rhs reference separate buffers (if any at all) after the construction. Additionally *this references the file which rhs did before the construction, and rhs references no file after the construction. The openmode, locale and any other state of rhs is also copied.
Postconditions: Let rhs_p refer to the state of rhs just prior to this construction and let rhs_a refer to the state of rhs just after this construction.
is_open() == rhs_p.is_open()
rhs_a.is_open() == false
gptr() - eback() == rhs_p.gptr() - rhs_p.eback()
egptr() - eback() == rhs_p.egptr() - rhs_p.eback()
pptr() - pbase() == rhs_p.pptr() - rhs_p.pbase()
epptr() - pbase() == rhs_p.epptr() - rhs_p.pbase()
if (eback()) eback() != rhs_a.eback()
if (gptr()) gptr() != rhs_a.gptr()
if (egptr()) egptr() != rhs_a.egptr()
if (pbase()) pbase() != rhs_a.pbase()
if (pptr()) pptr() != rhs_a.pptr()
if (epptr()) epptr() != rhs_a.epptr()
Effects: Destroys an object of class basic_filebuf<charT, traits>. Calls close(). If an exception occurs during the destruction of the object, including the call to close(), the exception is caught but not rethrown (see [res.on.exception.handling]).
basic_filebuf& operator=(basic_filebuf&& rhs);
Effects: Calls close() then move assigns from rhs. After the move assignment *this has the observable state it would have had if it had been move constructed from rhs (see [filebuf.cons]).
Returns: *this.
void swap(basic_filebuf& rhs);
Effects: Exchanges the state of *this and rhs.
template <class charT, class traits>
void swap(basic_filebuf<charT, traits>& x,
basic_filebuf<charT, traits>& y);
Effects: As if by x.swap(y).
Returns: true if a previous call to open succeeded (returned a non-null value) and there has been no intervening call to close.
basic_filebuf<charT, traits>* open(const char* s,
ios_base::openmode mode);
Effects: If is_open() != false, returns a null pointer. Otherwise, initializes the filebuf as required. It then opens a file, if possible, whose name is the ntbs s (as if by calling fopen(s, modstr)). The ntbs modstr is determined from mode & ~ios_base::ate as indicated in Table [tab:iostreams.file.open.modes]. If mode is not some combination of flags shown in the table then the open fails.
| ios_base flag combination | stdio equivalent | ||||
| binary | in | out | trunc | app | |
| + | "w" | ||||
| + | + | "a" | |||
| + | "a" | ||||
| + | + | "w" | |||
| + | "r" | ||||
| + | + | "r+" | |||
| + | + | + | "w+" | ||
| + | + | + | "a+" | ||
| + | + | "a+" | |||
| + | + | "wb" | |||
| + | + | + | "ab" | ||
| + | + | "ab" | |||
| + | + | + | "wb" | ||
| + | + | "rb" | |||
| + | + | + | "r+b" | ||
| + | + | + | + | "w+b" | |
| + | + | + | + | "a+b" | |
| + | + | + | "a+b" | ||
If the open operation succeeds and (mode & ios_base::ate) != 0, positions the file to the end (as if by calling fseek(file, 0, SEEK_END)).330
If the repositioning operation fails, calls close() and returns a null pointer to indicate failure.
Returns: this if successful, a null pointer otherwise.
basic_filebuf<charT, traits>* open(const string& s,
ios_base::openmode mode);
Returns: open(s.c_str(), mode);
basic_filebuf<charT, traits>* close();
Effects: If is_open() == false, returns a null pointer. If a put area exists, calls overflow(traits::eof()) to flush characters. If the last virtual member function called on *this (between underflow, overflow, seekoff, and seekpos) was overflow then calls a_codecvt.unshift (possibly several times) to determine a termination sequence, inserts those characters and calls overflow(traits::eof()) again. Finally, regardless of whether any of the preceding calls fails or throws an exception, the function closes the file (as if by calling fclose(file)). If any of the calls made by the function, including fclose, fails, close fails by returning a null pointer. If one of these calls throws an exception, the exception is caught and rethrown after closing the file.
Returns: this on success, a null pointer otherwise.
Postconditions: is_open() == false.
The macro SEEK_END is defined, and the function signatures fopen(const char*, const char*) and fseek(FILE*, long, int) are declared, in <cstdio> ([cstdio.syn]).
streamsize showmanyc() override;
Effects: Behaves the same as basic_streambuf::showmanyc() ([streambuf.virtuals]).
Remarks: An implementation might well provide an overriding definition for this function signature if it can determine that more characters can be read from the input sequence.
int_type underflow() override;
Effects: Behaves according to the description of basic_streambuf<charT, traits>::underflow(), with the specialization that a sequence of characters is read from the input sequence as if by reading from the associated file into an internal buffer ( extern_buf) and then as if by doing:
char extern_buf[XSIZE];
char* extern_end;
charT intern_buf[ISIZE];
charT* intern_end;
codecvt_base::result r =
a_codecvt.in(state, extern_buf, extern_buf+XSIZE, extern_end,
intern_buf, intern_buf+ISIZE, intern_end);
This shall be done in such a way that the class can recover the position (fpos_t) corresponding to each character between intern_buf and intern_end. If the value of r indicates that a_codecvt.in() ran out of space in intern_buf, retry with a larger intern_buf.
Effects: Behaves according to the description of basic_streambuf<charT, traits>::uflow(), with the specialization that a sequence of characters is read from the input with the same method as used by underflow.
int_type pbackfail(int_type c = traits::eof()) override;
Effects: Puts back the character designated by c to the input sequence, if possible, in one of three ways:
If traits::eq_int_type(c, traits::eof()) returns false and if the function makes a putback position available and if traits::eq(to_char_type(c), gptr()[-1]) returns true, decrements the next pointer for the input sequence, gptr().
Returns: c.
If traits::eq_int_type(c, traits::eof()) returns false and if the function makes a putback position available and if the function is permitted to assign to the putback position, decrements the next pointer for the input sequence, and stores c there.
Returns: c.
If traits::eq_int_type(c, traits::eof()) returns true, and if either the input sequence has a putback position available or the function makes a putback position available, decrements the next pointer for the input sequence, gptr().
Returns: traits::not_eof(c).
Returns: traits::eof() to indicate failure.
Remarks: If is_open() == false, the function always fails.
The function does not put back a character directly to the input sequence.
If the function can succeed in more than one of these ways, it is unspecified which way is chosen. The function can alter the number of putback positions available as a result of any call.
int_type overflow(int_type c = traits::eof()) override;
Effects: Behaves according to the description of basic_streambuf<charT, traits>::overflow(c), except that the behavior of “consuming characters” is performed by first converting as if by:
charT* b = pbase(); charT* p = pptr(); charT* end; char xbuf[XSIZE]; char* xbuf_end; codecvt_base::result r = a_codecvt.out(state, b, p, end, xbuf, xbuf+XSIZE, xbuf_end);
and then
If r == codecvt_base::error then fail.
If r == codecvt_base::noconv then output characters from b up to (and not including) p.
If r == codecvt_base::partial then output to the file characters from xbuf up to xbuf_end, and repeat using characters from end to p. If output fails, fail (without repeating).
Otherwise output from xbuf to xbuf_end, and fail if output fails. At this point if b != p and b == end (xbuf isn't large enough) then increase XSIZE and repeat from the beginning.
Returns: traits::not_eof(c) to indicate success, and traits::eof() to indicate failure. If is_open() == false, the function always fails.
basic_streambuf* setbuf(char_type* s, streamsize n) override;
pos_type seekoff(off_type off, ios_base::seekdir way,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
Effects: Let width denote a_codecvt.encoding(). If is_open() == false, or off != 0 && width <= 0, then the positioning operation fails. Otherwise, if way != basic_ios::cur or off != 0, and if the last operation was output, then update the output sequence and write any unshift sequence. Next, seek to the new position: if width > 0, call fseek(file, width * off, whence), otherwise call fseek(file, 0, whence).
Remarks: “The last operation was output” means either the last virtual operation was overflow or the put buffer is non-empty. “Write any unshift sequence” means, if width if less than zero then call a_codecvt.unshift(state, xbuf, xbuf+XSIZE, xbuf_end) and output the resulting unshift sequence. The function determines one of three values for the argument whence, of type int, as indicated in Table [tab:iostreams.seekoff.effects].
| way Value | stdio Equivalent |
| basic_ios::beg | SEEK_SET |
| basic_ios::cur | SEEK_CUR |
| basic_ios::end | SEEK_END |
Returns: A newly constructed pos_type object that stores the resultant stream position, if possible. If the positioning operation fails, or if the object cannot represent the resultant stream position, returns pos_type(off_type(-1)).
pos_type seekpos(pos_type sp,
ios_base::openmode which
= ios_base::in | ios_base::out) override;
Alters the file position, if possible, to correspond to the position stored in sp (as described below). Altering the file position performs as follows:
if (om & ios_base::out) != 0, then update the output sequence and write any unshift sequence;
set the file position to sp as if by a call to fsetpos;
if (om & ios_base::in) != 0, then update the input sequence;
where om is the open mode passed to the last call to open(). The operation fails if is_open() returns false.
If sp is an invalid stream position, or if the function positions neither sequence, the positioning operation fails. If sp has not been obtained by a previous successful call to one of the positioning functions (seekoff or seekpos) on the same file the effects are undefined.
Returns: sp on success. Otherwise returns pos_type(off_type(-1)).
void imbue(const locale& loc) override;
Requires: If the file is not positioned at its beginning and the encoding of the current locale as determined by a_codecvt.encoding() is state-dependent ([locale.codecvt.virtuals]) then that facet is the same as the corresponding facet of loc.
Effects: Causes characters inserted or extracted after this call to be converted according to loc until another call of imbue.
Remarks: This may require reconversion of previously converted characters. This in turn may require the implementation to be able to reconstruct the original contents of the file.
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ifstream
: public basic_istream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [ifstream.cons], constructors
basic_ifstream();
explicit basic_ifstream(const char* s,
ios_base::openmode mode = ios_base::in);
explicit basic_ifstream(const string& s,
ios_base::openmode mode = ios_base::in);
basic_ifstream(const basic_ifstream& rhs) = delete;
basic_ifstream(basic_ifstream&& rhs);
// [ifstream.assign], assign and swap
basic_ifstream& operator=(const basic_ifstream& rhs) = delete;
basic_ifstream& operator=(basic_ifstream&& rhs);
void swap(basic_ifstream& rhs);
// [ifstream.members], members
basic_filebuf<charT, traits>* rdbuf() const;
bool is_open() const;
void open(const char* s, ios_base::openmode mode = ios_base::in);
void open(const string& s, ios_base::openmode mode = ios_base::in);
void close();
private:
basic_filebuf<charT, traits> sb; // exposition only
};
template <class charT, class traits>
void swap(basic_ifstream<charT, traits>& x,
basic_ifstream<charT, traits>& y);
}
The class basic_ifstream<charT, traits> supports reading from named files. It uses a basic_filebuf<charT, traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as:
sb, the filebuf object.
Effects: Constructs an object of class basic_ifstream<charT, traits>, initializing the base class with basic_istream(&sb) and initializing sb with basic_filebuf<charT, traits>()) ([istream.cons], [filebuf.cons]).
explicit basic_ifstream(const char* s,
ios_base::openmode mode = ios_base::in);
Effects: Constructs an object of class basic_ifstream, initializing the base class with basic_istream(&sb) and initializing sb with basic_filebuf<charT, traits>()) ([istream.cons], [filebuf.cons]), then calls rdbuf()->open(s, mode | ios_base::in). If that function returns a null pointer, calls setstate(failbit).
explicit basic_ifstream(const string& s,
ios_base::openmode mode = ios_base::in);
Effects: The same as basic_ifstream(s.c_str(), mode).
basic_ifstream(basic_ifstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_filebuf. Next basic_istream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_filebuf.
basic_ifstream& operator=(basic_ifstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_ifstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_istream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits>
void swap(basic_ifstream<charT, traits>& x,
basic_ifstream<charT, traits>& y);
Effects: As if by x.swap(y).
basic_filebuf<charT, traits>* rdbuf() const;
Returns: const_cast<basic_filebuf<charT, traits>*>(&sb).
Returns: rdbuf()->is_open().
void open(const char* s, ios_base::openmode mode = ios_base::in);
Effects: Calls rdbuf()->open(s, mode | ios_base::in). If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
void open(const string& s, ios_base::openmode mode = ios_base::in);
Effects: Calls open(s.c_str(), mode).
Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_ofstream
: public basic_ostream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [ofstream.cons], constructors
basic_ofstream();
explicit basic_ofstream(const char* s,
ios_base::openmode mode = ios_base::out);
explicit basic_ofstream(const string& s,
ios_base::openmode mode = ios_base::out);
basic_ofstream(const basic_ofstream& rhs) = delete;
basic_ofstream(basic_ofstream&& rhs);
// [ofstream.assign], assign and swap
basic_ofstream& operator=(const basic_ofstream& rhs) = delete;
basic_ofstream& operator=(basic_ofstream&& rhs);
void swap(basic_ofstream& rhs);
// [ofstream.members], members
basic_filebuf<charT, traits>* rdbuf() const;
bool is_open() const;
void open(const char* s, ios_base::openmode mode = ios_base::out);
void open(const string& s, ios_base::openmode mode = ios_base::out);
void close();
private:
basic_filebuf<charT, traits> sb; // exposition only
};
template <class charT, class traits>
void swap(basic_ofstream<charT, traits>& x,
basic_ofstream<charT, traits>& y);
}
The class basic_ofstream<charT, traits> supports writing to named files. It uses a basic_filebuf<charT, traits> object to control the associated sequence. For the sake of exposition, the maintained data is presented here as:
sb, the filebuf object.
Effects: Constructs an object of class basic_ofstream<charT, traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_filebuf<charT, traits>()) ([ostream.cons], [filebuf.cons]).
explicit basic_ofstream(const char* s,
ios_base::openmode mode = ios_base::out);
Effects: Constructs an object of class basic_ofstream<charT, traits>, initializing the base class with basic_ostream(&sb) and initializing sb with basic_filebuf<charT, traits>()) ([ostream.cons], [filebuf.cons]), then calls rdbuf()->open(s, mode | ios_base::out). If that function returns a null pointer, calls setstate(failbit).
explicit basic_ofstream(const string& s,
ios_base::openmode mode = ios_base::out);
Effects: The same as basic_ofstream(s.c_str(), mode).
basic_ofstream(basic_ofstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_filebuf. Next basic_ostream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_filebuf.
basic_ofstream& operator=(basic_ofstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_ofstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_ostream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits>
void swap(basic_ofstream<charT, traits>& x,
basic_ofstream<charT, traits>& y);
Effects: As if by x.swap(y).
basic_filebuf<charT, traits>* rdbuf() const;
Returns: const_cast<basic_filebuf<charT, traits>*>(&sb).
Returns: rdbuf()->is_open().
void open(const char* s, ios_base::openmode mode = ios_base::out);
Effects: Calls rdbuf()->open(s, mode | ios_base::out). If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
Effects: Calls rdbuf()->close() and, if that function fails (returns a null pointer), calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
void open(const string& s, ios_base::openmode mode = ios_base::out);
Effects: Calls open(s.c_str(), mode).
namespace std {
template <class charT, class traits = char_traits<charT>>
class basic_fstream
: public basic_iostream<charT, traits> {
public:
using char_type = charT;
using int_type = typename traits::int_type;
using pos_type = typename traits::pos_type;
using off_type = typename traits::off_type;
using traits_type = traits;
// [fstream.cons], constructors
basic_fstream();
explicit basic_fstream(
const char* s,
ios_base::openmode mode = ios_base::in | ios_base::out);
explicit basic_fstream(
const string& s,
ios_base::openmode mode = ios_base::in | ios_base::out);
basic_fstream(const basic_fstream& rhs) = delete;
basic_fstream(basic_fstream&& rhs);
// [fstream.assign], assign and swap
basic_fstream& operator=(const basic_fstream& rhs) = delete;
basic_fstream& operator=(basic_fstream&& rhs);
void swap(basic_fstream& rhs);
// [fstream.members], members
basic_filebuf<charT, traits>* rdbuf() const;
bool is_open() const;
void open(
const char* s,
ios_base::openmode mode = ios_base::in | ios_base::out);
void open(
const string& s,
ios_base::openmode mode = ios_base::in | ios_base::out);
void close();
private:
basic_filebuf<charT, traits> sb; // exposition only
};
template <class charT, class traits>
void swap(basic_fstream<charT, traits>& x,
basic_fstream<charT, traits>& y);
}
The class template basic_fstream<charT, traits> supports reading and writing from named files. It uses a basic_filebuf<charT, traits> object to control the associated sequences. For the sake of exposition, the maintained data is presented here as:
sb, the basic_filebuf object.
Effects: Constructs an object of class basic_fstream<charT, traits>, initializing the base class with basic_iostream(&sb) and initializing sb with basic_filebuf<charT, traits>().
explicit basic_fstream(
const char* s,
ios_base::openmode mode = ios_base::in | ios_base::out);
Effects: Constructs an object of class basic_fstream<charT, traits>, initializing the base class with basic_iostream(&sb) and initializing sb with basic_filebuf<charT, traits>(). Then calls rdbuf()->open(s, mode). If that function returns a null pointer, calls setstate(failbit).
explicit basic_fstream(
const string& s,
ios_base::openmode mode = ios_base::in | ios_base::out);
Effects: The same as basic_fstream(s.c_str(), mode).
basic_fstream(basic_fstream&& rhs);
Effects: Move constructs from the rvalue rhs. This is accomplished by move constructing the base class, and the contained basic_filebuf. Next basic_istream<charT, traits>::set_rdbuf(&sb) is called to install the contained basic_filebuf.
basic_fstream& operator=(basic_fstream&& rhs);
Effects: Move assigns the base and members of *this from the base and corresponding members of rhs.
Returns: *this.
void swap(basic_fstream& rhs);
Effects: Exchanges the state of *this and rhs by calling basic_iostream<charT, traits>::swap(rhs) and sb.swap(rhs.sb).
template <class charT, class traits>
void swap(basic_fstream<charT, traits>& x,
basic_fstream<charT, traits>& y);
Effects: As if by x.swap(y).
basic_filebuf<charT, traits>* rdbuf() const;
Returns: const_cast<basic_filebuf<charT, traits>*>(&sb).
Returns: rdbuf()->is_open().
void open(
const char* s,
ios_base::openmode mode = ios_base::in | ios_base::out);
Effects: Calls rdbuf()->open(s, mode). If that function does not return a null pointer calls clear(), otherwise calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
void open(
const string& s,
ios_base::openmode mode = ios_base::in | ios_base::out);
Effects: Calls open(s.c_str(), mode).
Effects: Calls rdbuf()->close() and, if that function returns a null pointer, calls setstate(failbit) (which may throw ios_base::failure) ([iostate.flags]).
This subclause describes operations on file systems and their components, such as paths, regular files, and directories.
Conformance is specified in terms of behavior. Ideal behavior is not always implementable, so the conformance subclauses take that into account.
Some behavior is specified by reference to POSIX ([fs.norm.ref]). How such behavior is actually implemented is unspecified. [ Note: This constitutes an “as if” rule allowing implementations to call native operating system or other APIs. — end note ]
Implementations are encouraged to provide such behavior as it is defined by POSIX. Implementations shall document any behavior that differs from the behavior defined by POSIX. Implementations that do not support exact POSIX behavior are encouraged to provide behavior as close to POSIX behavior as is reasonable given the limitations of actual operating systems and file systems. If an implementation cannot provide any reasonable behavior, the implementation shall report an error as specified in [fs.err.report]. [ Note: This allows users to rely on an exception being thrown or an error code being set when an implementation cannot provide any reasonable behavior. — end note ]
Implementations are not required to provide behavior that is not supported by a particular file system. [ Example: The FAT file system used by some memory cards, camera memory, and floppy disks does not support hard links, symlinks, and many other features of more capable file systems, so implementations are not required to support those features on the FAT file system. — end example ]
Some behavior is specified as being operating system dependent ([fs.def.osdep]). The operating system an implementation is dependent upon is implementation-defined.
It is permissible for an implementation to be dependent upon an operating system emulator rather than the actual underlying operating system.
Behavior is undefined if calls to functions provided by this subclause introduce a file system race ([fs.def.race]).
If the possibility of a file system race would make it unreliable for a program to test for a precondition before calling a function described herein, Requires: is not specified for the function. [ Note: As a design practice, preconditions are not specified when it is unreasonable for a program to detect them prior to calling the function. — end note ]
POSIX® is a registered trademark of The IEEE. Windows® is a registered trademark of Microsoft Corporation. This information is given for the convenience of users of this document and does not constitute an endorsement by ISO or IEC of these products.
A path that unambiguously identifies the location of a file without reference to an additional starting location. The elements of a path that determine if it is absolute are operating system dependent.
An absolute path that has no elements that are symbolic links, and no dot or dot-dot elements ([path.generic]).
A file within a file system that acts as a container of directory entries that contain information about other files, possibly including other directory files.
An object within a file system that holds user or system data. Files can be written to, or read from, or both. A file has certain attributes, including type. File types include regular files and directories. Other types of files, such as symbolic links ([fs.def.symlink]), may be supported by the implementation.
A collection of files and certain of their attributes.
The condition that occurs when multiple threads, processes, or computers interleave access and modification of the same object within a file system.
The name of a file. Filenames dot and dot-dot have special meaning. The following characteristics of filenames are operating system dependent:
The permitted characters. [ Example: Some operating systems prohibit the ASCII control characters (0x00 – 0x1F) in filenames. — end example ]
The maximum permitted length.
Filenames that are not permitted.
Filenames that have special meaning.
Case awareness and sensitivity during path resolution.
Special rules that may apply to file types other than regular files, such as directories.
A link ([fs.def.link]) to an existing file. Some file systems support multiple hard links to a file. If the last hard link to a file is removed, the file itself is removed. [ Note: A hard link can be thought of as a shared-ownership smart pointer to a file. — end note ]
A directory entry that associates a filename with a file. A link is either a hard link ([fs.def.hardlink]) or a symbolic link ([fs.def.symlink]).
For narrow character strings, the operating system dependent current encoding for pathnames ([fs.def.pathname]). For wide character strings, the implementation defined execution wide-character set encoding ([lex.charset]).
The operating system dependent pathname format accepted by the host operating system.
A path with no redundant current directory (dot) elements, no redundant parent directory (dot-dot) elements, and no redundant directory-separators. The normal form for an empty path is an empty path. The normal form for a path ending in a directory-separator that is not the root directory has a current directory (dot) element appended. A path in normal form is said to be normalized. The process of obtaining a normalized path from a path that is not in normal form is called normalization. [ Note: The rule that appends a current directory (dot) element supports operating systems like OpenVMS that use different syntax for directory names and regular file names. — end note ]
Behavior that is dependent upon the behavior and characteristics of an operating system. See [fs.conform.os].
⟨of a directory⟩ the directory that both contains a directory entry for the given directory and is represented by the filename dot-dot in the given directory.
⟨of other types of files⟩ a directory containing a directory entry for the file under discussion.
A sequence of elements that identify the location of a file within a filesystem. The elements are the root-nameopt, root-directoryopt, and an optional sequence of filenames. The maximum number of elements in the sequence is operating system dependent.
A character string that represents the name of a path. Pathnames are formatted according to the generic pathname format grammar ([path.generic]) or an operating system dependent native pathname format.
Pathname resolution is the operating system dependent mechanism for resolving a pathname to a particular file in a file hierarchy. There may be multiple pathnames that resolve to the same file. [ Example: POSIX specifies the mechanism in section 4.11, Pathname resolution. — end example ]
A path that is not absolute, and as such, only unambiguously identifies the location of a file when resolved ([fs.def.pathres]) relative to an implied starting location. The elements of a path that determine if it is relative are operating system dependent. [ Note: Pathnames “.” and “..” are relative paths. — end note ]
A type of file with the property that when the file is encountered during pathname resolution, a string stored by the file is used to modify the pathname resolution. [ Note: Symbolic links are often called symlinks. A symbolic link can be thought of as a raw pointer to a file. If the file pointed to does not exist, the symbolic link is said to be a “dangling” symbolic link. — end note ]
Throughout this subclause, char, wchar_t, char16_t, and char32_t are collectively called encoded character types.
Functions with template parameters named EcharT shall not participate in overload resolution unless EcharT is one of the encoded character types.
Template parameters named InputIterator shall meet the input iterator requirements ([input.iterators]) and shall have a value type that is one of the encoded character types.
[ Note: Use of an encoded character type implies an associated encoding. Since signed char and unsigned char have no implied encoding, they are not included as permitted types. — end note ]
Template parameters named Allocator shall meet the Allocator requirements ([allocator.requirements]).
Unless otherwise specified, references to entities described in this subclause are assumed to be qualified with ::std::filesystem::.
namespace std::filesystem {
// [class.path], paths
class path;
// [path.non-member], path non-member functions
void swap(path& lhs, path& rhs) noexcept;
size_t hash_value(const path& p) noexcept;
bool operator==(const path& lhs, const path& rhs) noexcept;
bool operator!=(const path& lhs, const path& rhs) noexcept;
bool operator< (const path& lhs, const path& rhs) noexcept;
bool operator<=(const path& lhs, const path& rhs) noexcept;
bool operator> (const path& lhs, const path& rhs) noexcept;
bool operator>=(const path& lhs, const path& rhs) noexcept;
path operator/ (const path& lhs, const path& rhs);
// [path.io], path inserter and extractor
template <class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const path& p);
template <class charT, class traits>
basic_istream<charT, traits>&
operator>>(basic_istream<charT, traits>& is, path& p);
// [path.factory], path factory functions
template <class Source>
path u8path(const Source& source);
template <class InputIterator>
path u8path(InputIterator first, InputIterator last);
// [class.filesystem_error], filesystem errors
class filesystem_error;
// [class.directory_entry], directory entries
class directory_entry;
// [class.directory_iterator], directory iterators
class directory_iterator;
// [directory_iterator.nonmembers], range access for directory iterators
directory_iterator begin(directory_iterator iter) noexcept;
directory_iterator end(const directory_iterator&) noexcept;
// [class.rec.dir.itr], recursive directory iterators
class recursive_directory_iterator;
// [rec.dir.itr.nonmembers], range access for recursive directory iterators
recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept;
recursive_directory_iterator end(const recursive_directory_iterator&) noexcept;
// [class.file_status], file status
class file_status;
struct space_info {
uintmax_t capacity;
uintmax_t free;
uintmax_t available;
};
// [fs.enum], enumerations
enum class file_type;
enum class perms;
enum class copy_options;
enum class directory_options;
using file_time_type = chrono::time_point<trivial-clock>;
// [fs.op.funcs], filesystem operations
path absolute(const path& p, const path& base = current_path());
path canonical(const path& p, const path& base = current_path());
path canonical(const path& p, error_code& ec);
path canonical(const path& p, const path& base, error_code& ec);
void copy(const path& from, const path& to);
void copy(const path& from, const path& to, error_code& ec) noexcept;
void copy(const path& from, const path& to, copy_options options);
void copy(const path& from, const path& to, copy_options options,
error_code& ec) noexcept;
bool copy_file(const path& from, const path& to);
bool copy_file(const path& from, const path& to, error_code& ec) noexcept;
bool copy_file(const path& from, const path& to, copy_options option);
bool copy_file(const path& from, const path& to, copy_options option,
error_code& ec) noexcept;
void copy_symlink(const path& existing_symlink, const path& new_symlink);
void copy_symlink(const path& existing_symlink, const path& new_symlink,
error_code& ec) noexcept;
bool create_directories(const path& p);
bool create_directories(const path& p, error_code& ec) noexcept;
bool create_directory(const path& p);
bool create_directory(const path& p, error_code& ec) noexcept;
bool create_directory(const path& p, const path& attributes);
bool create_directory(const path& p, const path& attributes,
error_code& ec) noexcept;
void create_directory_symlink(const path& to, const path& new_symlink);
void create_directory_symlink(const path& to, const path& new_symlink,
error_code& ec) noexcept;
void create_hard_link(const path& to, const path& new_hard_link);
void create_hard_link(const path& to, const path& new_hard_link,
error_code& ec) noexcept;
void create_symlink(const path& to, const path& new_symlink);
void create_symlink(const path& to, const path& new_symlink,
error_code& ec) noexcept;
path current_path();
path current_path(error_code& ec);
void current_path(const path& p);
void current_path(const path& p, error_code& ec) noexcept;
bool exists(file_status s) noexcept;
bool exists(const path& p);
bool exists(const path& p, error_code& ec) noexcept;
bool equivalent(const path& p1, const path& p2);
bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept;
uintmax_t file_size(const path& p);
uintmax_t file_size(const path& p, error_code& ec) noexcept;
uintmax_t hard_link_count(const path& p);
uintmax_t hard_link_count(const path& p, error_code& ec) noexcept;
bool is_block_file(file_status s) noexcept;
bool is_block_file(const path& p);
bool is_block_file(const path& p, error_code& ec) noexcept;
bool is_character_file(file_status s) noexcept;
bool is_character_file(const path& p);
bool is_character_file(const path& p, error_code& ec) noexcept;
bool is_directory(file_status s) noexcept;
bool is_directory(const path& p);
bool is_directory(const path& p, error_code& ec) noexcept;
bool is_empty(const path& p);
bool is_empty(const path& p, error_code& ec) noexcept;
bool is_fifo(file_status s) noexcept;
bool is_fifo(const path& p);
bool is_fifo(const path& p, error_code& ec) noexcept;
bool is_other(file_status s) noexcept;
bool is_other(const path& p);
bool is_other(const path& p, error_code& ec) noexcept;
bool is_regular_file(file_status s) noexcept;
bool is_regular_file(const path& p);
bool is_regular_file(const path& p, error_code& ec) noexcept;
bool is_socket(file_status s) noexcept;
bool is_socket(const path& p);
bool is_socket(const path& p, error_code& ec) noexcept;
bool is_symlink(file_status s) noexcept;
bool is_symlink(const path& p);
bool is_symlink(const path& p, error_code& ec) noexcept;
file_time_type last_write_time(const path& p);
file_time_type last_write_time(const path& p, error_code& ec) noexcept;
void last_write_time(const path& p, file_time_type new_time);
void last_write_time(const path& p, file_time_type new_time,
error_code& ec) noexcept;
void permissions(const path& p, perms prms);
void permissions(const path& p, perms prms, error_code& ec);
path proximate(const path& p, error_code& ec);
path proximate(const path& p, const path& base = current_path());
path proximate(const path& p, const path& base, error_code& ec);
path read_symlink(const path& p);
path read_symlink(const path& p, error_code& ec);
path relative(const path& p, error_code& ec);
path relative(const path& p, const path& base = current_path());
path relative(const path& p, const path& base, error_code& ec);
bool remove(const path& p);
bool remove(const path& p, error_code& ec) noexcept;
uintmax_t remove_all(const path& p);
uintmax_t remove_all(const path& p, error_code& ec) noexcept;
void rename(const path& from, const path& to);
void rename(const path& from, const path& to, error_code& ec) noexcept;
void resize_file(const path& p, uintmax_t size);
void resize_file(const path& p, uintmax_t size, error_code& ec) noexcept;
space_info space(const path& p);
space_info space(const path& p, error_code& ec) noexcept;
file_status status(const path& p);
file_status status(const path& p, error_code& ec) noexcept;
bool status_known(file_status s) noexcept;
file_status symlink_status(const path& p);
file_status symlink_status(const path& p, error_code& ec) noexcept;
path system_complete(const path& p);
path system_complete(const path& p, error_code& ec);
path temp_directory_path();
path temp_directory_path(error_code& ec);
path weakly_canonical(const path& p);
path weakly_canonical(const path& p, error_code& ec);
}
trivial-clock is an implementation-defined type that satisfies the TrivialClock requirements ([time.clock.req]) and that is capable of representing and measuring file time values. Implementations should ensure that the resolution and range of file_time_type reflect the operating system dependent resolution and range of file time values.
Filesystem library functions often provide two overloads, one that throws an exception to report file system errors, and another that sets an error_code. [ Note: This supports two common use cases:
Uses where file system errors are truly exceptional and indicate a serious failure. Throwing an exception is an appropriate response.
Uses where file system errors are routine and do not necessarily represent failure. Returning an error code is the most appropriate response. This allows application specific error handling, including simply ignoring the error.
— end note ]
Functions not having an argument of type error_code& handle errors as follows, unless otherwise specified:
When a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, an exception of type filesystem_error shall be thrown. For functions with a single path argument, that argument shall be passed to the filesystem_error constructor with a single path argument. For functions with two path arguments, the first of these arguments shall be passed to the filesystem_error constructor as the path1 argument, and the second shall be passed as the path2 argument. The filesystem_error constructor's error_code argument is set as appropriate for the specific operating system dependent error.
Failure to allocate storage is reported by throwing an exception as described in [res.on.exception.handling].
Destructors throw nothing.
Functions having an argument of type error_code& handle errors as follows, unless otherwise specified:
If a call by the implementation to an operating system or other underlying API results in an error that prevents the function from meeting its specifications, the error_code& argument is set as appropriate for the specific operating system dependent error. Otherwise, clear() is called on the error_code& argument.
An object of class path represents a path ([fs.def.path]) and contains a pathname ([fs.def.pathname]). Such an object is concerned only with the lexical and syntactic aspects of a path. The path does not necessarily exist in external storage, and the pathname is not necessarily valid for the current operating system or for a particular file system.
namespace std::filesystem {
class path {
public:
using value_type = see below;
using string_type = basic_string<value_type>;
static constexpr value_type preferred_separator = see below;
// [path.construct], constructors and destructor
path() noexcept;
path(const path& p);
path(path&& p) noexcept;
path(string_type&& source);
template <class Source>
path(const Source& source);
template <class InputIterator>
path(InputIterator first, InputIterator last);
template <class Source>
path(const Source& source, const locale& loc);
template <class InputIterator>
path(InputIterator first, InputIterator last, const locale& loc);
~path();
// [path.assign], assignments
path& operator=(const path& p);
path& operator=(path&& p) noexcept;
path& operator=(string_type&& source);
path& assign(string_type&& source);
template <class Source>
path& operator=(const Source& source);
template <class Source>
path& assign(const Source& source)
template <class InputIterator>
path& assign(InputIterator first, InputIterator last);
// [path.append], appends
path& operator/=(const path& p);
template <class Source>
path& operator/=(const Source& source);
template <class Source>
path& append(const Source& source);
template <class InputIterator>
path& append(InputIterator first, InputIterator last);
// [path.concat], concatenation
path& operator+=(const path& x);
path& operator+=(const string_type& x);
path& operator+=(basic_string_view<value_type> x);
path& operator+=(const value_type* x);
path& operator+=(value_type x);
template <class Source>
path& operator+=(const Source& x);
template <class EcharT>
path& operator+=(EcharT x);
template <class Source>
path& concat(const Source& x);
template <class InputIterator>
path& concat(InputIterator first, InputIterator last);
// [path.modifiers], modifiers
void clear() noexcept;
path& make_preferred();
path& remove_filename();
path& replace_filename(const path& replacement);
path& replace_extension(const path& replacement = path());
void swap(path& rhs) noexcept;
// [path.native.obs], native format observers
const string_type& native() const noexcept;
const value_type* c_str() const noexcept;
operator string_type() const;
template <class EcharT, class traits = char_traits<EcharT>,
class Allocator = allocator<EcharT>>
basic_string<EcharT, traits, Allocator>
string(const Allocator& a = Allocator()) const;
std::string string() const;
std::wstring wstring() const;
std::string u8string() const;
std::u16string u16string() const;
std::u32string u32string() const;
// [path.generic.obs], generic format observers
template <class EcharT, class traits = char_traits<EcharT>,
class Allocator = allocator<EcharT>>
basic_string<EcharT, traits, Allocator>
generic_string(const Allocator& a = Allocator()) const;
std::string generic_string() const;
std::wstring generic_wstring() const;
std::string generic_u8string() const;
std::u16string generic_u16string() const;
std::u32string generic_u32string() const;
// [path.compare], compare
int compare(const path& p) const noexcept;
int compare(const string_type& s) const;
int compare(basic_string_view<value_type> s) const;
int compare(const value_type* s) const;
// [path.decompose], decomposition
path root_name() const;
path root_directory() const;
path root_path() const;
path relative_path() const;
path parent_path() const;
path filename() const;
path stem() const;
path extension() const;
// [path.query], query
bool empty() const noexcept;
bool has_root_name() const;
bool has_root_directory() const;
bool has_root_path() const;
bool has_relative_path() const;
bool has_parent_path() const;
bool has_filename() const;
bool has_stem() const;
bool has_extension() const;
bool is_absolute() const;
bool is_relative() const;
// [path.gen], generation
path lexically_normal() const;
path lexically_relative(const path& base) const;
path lexically_proximate(const path& base) const;
// [path.itr], iterators
class iterator;
using const_iterator = iterator;
iterator begin() const;
iterator end() const;
private:
string_type pathstring; // exposition only
};
}
value_type is a typedef for the operating system dependent encoded character type used to represent pathnames.
The value of preferred_separator is the operating system dependent preferred-separator character ([path.generic]).
[ Example: For POSIX-based operating systems, value_type is char and preferred_separator is the slash character ('/'). For Windows-based operating systems, value_type is wchar_t and preferred_separator is the backslash character (L'\\'). — end example ]
pathname: root-name root-directoryopt relative-pathopt root-directory relative-pathopt relative-path
root-name: An operating system dependent name that identifies the starting location for absolute paths. [ Note: Many operating systems define a name beginning with two directory-separator characters as a root-name that identifies network or other resource locations. Some operating systems define a single letter followed by a colon as a drive specifier – a root-name identifying a specific device such as a disk drive. — end note ]
root-directory: directory-separator
relative-path: filename relative-path directory-separator relative-path directory-separator filename
filename: name dot dot-dot
name: A sequence of characters other than directory-separator characters. [ Note: Operating systems often place restrictions on the characters that may be used in a filename. For wide portability, users may wish to limit filename characters to the POSIX Portable Filename Character Set:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
a b c d e f g h i j k l m n o p q r s t u v w x y z
0 1 2 3 4 5 6 7 8 9 . _ - — end note ]
dot: The filename consisting solely of a single period character (.).
dot-dot: The filename consisting solely of two period characters (..).
directory-separator: slash slash directory-separator preferred-separator preferred-separator directory-separator
preferred-separator: An operating system dependent directory separator character. May be a synonym for slash.
slash: The slash character (/).
Multiple successive directory-separator characters are considered to be the same as one directory-separator character.
The filename dot is treated as a reference to the current directory. The filename dot-dot is treated as a reference to the parent directory. What the filename dot-dot refers to relative to root-directory is implementation-defined. Specific filenames may have special meanings for a particular operating system.
[ Note: The format conversions described in this section are not applied on POSIX- or Windows-based operating systems because on these systems:
The generic format is acceptable as a native path.
There is no need to distinguish between native format and generic format in function arguments.
Paths for regular files and paths for directories share the same syntax.
— end note ]
Function arguments that take character sequences representing paths may use the generic pathname format grammar ([path.generic]) or the native pathname format ([fs.def.native]). If and only if such arguments are in the generic format and the generic format is not acceptable to the operating system as a native path, conversion to native format shall be performed during the processing of the argument.
[ Note: Some operating systems may have no unambiguous way to distinguish between native format and generic format arguments. This is by design as it simplifies use for operating systems that do not require disambiguation. An implementation for an operating system where disambiguation is required is permitted to distinguish between the formats. — end note ]
If the native format requires paths for regular files to be formatted differently from paths for directories, the path shall be treated as a directory path if its last element is a directory-separator, otherwise it shall be treated as a path to a regular file.
For member function arguments that take character sequences representing paths and for member functions returning strings, value type and encoding conversion is performed if the value type of the argument or return value differs from path::value_type. For the argument or return value, the method of conversion and the encoding to be converted to is determined by its value type:
char: The encoding is the native narrow encoding ([fs.def.native.encode]). The method of conversion, if any, is operating system dependent. [ Note: For POSIX-based operating systems path::value_type is char so no conversion from char value type arguments or to char value type return values is performed. For Windows-based operating systems, the native narrow encoding is determined by calling a Windows API function. — end note ] [ Note: This results in behavior identical to other C and C++ standard library functions that perform file operations using narrow character strings to identify paths. Changing this behavior would be surprising and error prone. — end note ]
wchar_t: The encoding is the native wide encoding ([fs.def.native.encode]). The method of conversion is unspecified. [ Note: For Windows-based operating systems path::value_type is wchar_t so no conversion from wchar_t value type arguments or to wchar_t value type return values is performed. — end note ]
char16_t: The encoding is UTF-16. The method of conversion is unspecified.
char32_t: The encoding is UTF-32. The method of conversion is unspecified.
If the encoding being converted to has no representation for source characters, the resulting converted characters, if any, are unspecified.
In addition to the requirements ([fs.req]), function template parameters named Source shall be one of:
basic_string<EcharT, traits, Allocator>. A function argument const Source& source shall have an effective range [source.begin(), source.end()).
basic_string_view<EcharT, traits>. A function argument const Source& source shall have an effective range [source.begin(), source.end()).
A type meeting the input iterator requirements that iterates over a NTCTS. The value type shall be an encoded character type. A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_traits<Source>::value_type().
A character array that after array-to-pointer decay results in a pointer to the start of a NTCTS. The value type shall be an encoded character type. A function argument const Source& source shall have an effective range [source, end) where end is the first iterator value with an element value equal to iterator_traits<decay_t<Source>>::value_type().
Functions taking template parameters named Source shall not participate in overload resolution unless either Source is a specialization of basic_string or basic_string_view or the qualified-id iterator_traits<decay_t<Source>>::value_type is valid and denotes a possibly const encoded character type ([temp.deduct]).
[ Note: See path conversions ([path.cvt]) for how the value types above and their encodings convert to path::value_type and its encoding. — end note ]
Arguments of type Source shall not be null pointers.
Effects: Constructs an object of class path.
Postconditions: empty() == true.
path(const path& p);
path(path&& p) noexcept;
Effects: Constructs an object of class path with pathstring having the original value of p.pathstring. In the second form, p is left in a valid but unspecified state.
Effects: Constructs an object of class path with pathstring having the original value of source. source is left in a valid but unspecified state.
template <class Source>
path(const Source& source);
template <class InputIterator>
path(InputIterator first, InputIterator last);
Effects: Constructs an object of class path, storing the effective range of source ([path.req]) or the range [first, last) in pathstring, converting format and encoding if required ([path.cvt]).
template <class Source>
path(const Source& source, const locale& loc);
template <class InputIterator>
path(InputIterator first, InputIterator last, const locale& loc);
Requires: The value type of Source and InputIterator is char.
Effects: Constructs an object of class path, storing the effective range of source or the range [first, last) in pathstring, after converting format if required and after converting the encoding as follows:
If value_type is wchar_t, converts to the native wide encoding ([fs.def.native.encode]) using the codecvt<wchar_t, char, mbstate_t> facet of loc.
Otherwise a conversion is performed using the codecvt<wchar_t, char, mbstate_t> facet of loc, and then a second conversion to the current narrow encoding.
[ Example: A string is to be read from a database that is encoded in ISO/IEC 8859-1, and used to create a directory:
namespace fs = std::filesystem; std::string latin1_string = read_latin1_data(); codecvt_8859_1<wchar_t> latin1_facet; std::locale latin1_locale(std::locale(), latin1_facet); fs::create_directory(fs::path(latin1_string, latin1_locale));
For POSIX-based operating systems, the path is constructed by first using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a wide character string in the native wide encoding ([fs.def.native.encode]). The resulting wide string is then converted to a narrow character pathstring string in the current native narrow encoding. If the native wide encoding is UTF-16 or UTF-32, and the current native narrow encoding is UTF-8, all of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation, but for other native narrow encodings some characters may have no representation.
For Windows-based operating systems, the path is constructed by using latin1_facet to convert ISO/IEC 8859-1 encoded latin1_string to a UTF-16 encoded wide character pathstring string. All of the characters in the ISO/IEC 8859-1 character set will be converted to their Unicode representation. — end example ]
path& operator=(const path& p);
Effects: If *this and p are the same object, has no effect. Otherwise, modifies pathstring to have the original value of p.pathstring.
Returns: *this.
path& operator=(path&& p) noexcept;
Effects: If *this and p are the same object, has no effect. Otherwise, modifies pathstring to have the original value of p.pathstring. p is left in a valid but unspecified state. [ Note: A valid implementation is swap(p). — end note ]
Returns: *this.
path& operator=(string_type&& source);
path& assign(string_type&& source);
Effects: Modifies pathstring to have the original value of source. source is left in a valid but unspecified state.
Returns: *this.
template <class Source>
path& operator=(const Source& source);
template <class Source>
path& assign(const Source& source);
template <class InputIterator>
path& assign(InputIterator first, InputIterator last);
Effects: Stores the effective range of source ([path.req]) or the range [first, last) in pathstring, converting format and encoding if required ([path.cvt]).
Returns: *this.
The append operations use operator/= to denote their semantic effect of appending preferred-separator when needed.
Requires: !p.has_root_name().
Effects: Appends path::preferred_separator to pathstring unless:
an added directory-separator would be redundant, or
an added directory-separator would change a relative path into an absolute path [ Note: An empty path is relative. — end note ], or
p.empty() is true, or
*p.native().cbegin() is a directory-separator.
Then appends p.native() to pathstring.
Returns: *this.
template <class Source>
path& operator/=(const Source& source);
template <class Source>
path& append(const Source& source);
Effects: Equivalent to: return operator/=(path(source));
template <class InputIterator>
path& append(InputIterator first, InputIterator last);
Effects: Equivalent to: return operator/=(path(first, last));
path& operator+=(const path& x);
path& operator+=(const string_type& x);
path& operator+=(basic_string_view<value_type> x);
path& operator+=(const value_type* x);
path& operator+=(value_type x);
template <class Source>
path& operator+=(const Source& x);
template <class EcharT>
path& operator+=(EcharT x);
template <class Source>
path& concat(const Source& x);
template <class InputIterator>
path& concat(InputIterator first, InputIterator last);
Postconditions: native() == prior_native + effective-argument, where prior_native is native() prior to the call to operator+=, and effective-argument is:
if x is present and is const path&, x.native(); otherwise,
if source is present, the effective range of source ([path.req]); otherwise,
if first and last are present, the range [first, last); otherwise,
x.
If the value type of effective-argument would not be path::value_type, the actual argument or argument range is first converted ([path.type.cvt]) so that effective-argument has value type path::value_type.
Returns: *this.
Postconditions: empty() == true.
Effects: Each directory-separator is converted to preferred-separator.
Returns: *this.
[ Example:
path p("foo/bar");
std::cout << p << '\n';
p.make_preferred();
std::cout << p << '\n';
On an operating system where preferred-separator is the same as directory-separator, the output is:
"foo/bar" "foo/bar"
On an operating system where preferred-separator is a backslash, the output is:
"foo/bar" "foo\bar"
— end example ]
Postconditions: !has_filename().
Returns: *this.
[ Example:
std::cout << path("/foo").remove_filename(); // outputs "/"
std::cout << path("/").remove_filename(); // outputs ""
— end example ]
path& replace_filename(const path& replacement);
Effects: Equivalent to:
remove_filename(); operator/=(replacement);
Returns: *this.
[ Example:
std::cout << path("/").replace_filename("bar"); // outputs "bar"
— end example ]
path& replace_extension(const path& replacement = path());
Effects: pathstring (the stored path) is modified as follows:
Any existing extension()([path.decompose]) is removed from the stored path, then
If replacement is not empty and does not begin with a dot character, a dot character is appended to the stored path, then
replacement is concatenated to the stored path.
Returns: *this.
void swap(path& rhs) noexcept;
Effects: Swaps the contents of the two paths pathstring and rhs.pathstring.
Complexity: Constant time.
The string returned by all native format observers is in the native pathname format ([fs.def.native]).
Returns: pathstring.
const value_type* c_str() const noexcept;
Returns: pathstring.c_str().
Returns: pathstring.
[ Note: Conversion to string_type is provided so that an object of class path can be given as an argument to existing standard library file stream constructors and open functions. — end note ]
template <class EcharT, class traits = char_traits<EcharT>,
class Allocator = allocator<EcharT>>
basic_string<EcharT, traits, Allocator>
string(const Allocator& a = Allocator()) const;
Returns: pathstring.
Remarks: All memory allocation, including for the return value, shall be performed by a. Conversion, if any, is specified by [path.cvt].
std::string string() const;
std::wstring wstring() const;
std::string u8string() const;
std::u16string u16string() const;
std::u32string u32string() const;
Returns: pathstring.
Remarks: Conversion, if any, is performed as specified by [path.cvt]. The encoding of the string returned by u8string() is always UTF-8.
Generic format observer functions return strings formatted according to the generic pathname format ([path.generic]). The forward slash ('/') character is used as the directory-separator character.
[ Example: On an operating system that uses backslash as its preferred-separator, path("foo\\bar").generic_string() returns "foo/bar". — end example ]
template <class EcharT, class traits = char_traits<EcharT>,
class Allocator = allocator<EcharT>>
basic_string<EcharT, traits, Allocator>
generic_string(const Allocator& a = Allocator()) const;
Returns: pathstring, reformatted according to the generic pathname format ([path.generic]).
Remarks: All memory allocation, including for the return value, shall be performed by a. Conversion, if any, is specified by [path.cvt].
std::string generic_string() const;
std::wstring generic_wstring() const;
std::string generic_u8string() const;
std::u16string generic_u16string() const;
std::u32string generic_u32string() const;
Returns: pathstring, reformatted according to the generic pathname format ([path.generic]).
Remarks: Conversion, if any, is specified by [path.cvt]. The encoding of the string returned by generic_u8string() is always UTF-8.
int compare(const path& p) const noexcept;
Returns:
A value less than 0, if native() for the elements of *this are lexicographically less than native() for the elements of p; otherwise,
a value greater than 0, if native() for the elements of *this are lexicographically greater than native() for the elements of p; otherwise,
0.
Remarks: The elements are determined as if by iteration over the half-open range [begin(), end()) for *this and p.
int compare(const string_type& s) const
int compare(basic_string_view<value_type> s) const;
Returns: compare(path(s)).
int compare(const value_type* s) const
Returns: compare(path(s)).
Returns: root-directory, if pathstring includes root-directory, otherwise path().
Returns: root_name() / root_directory().
Returns: A path composed from pathstring, if !empty(), beginning with the first filename after root-path. Otherwise, path().
Returns: (empty() || begin() == --end()) ? path() : pp, where pp is constructed as if by starting with an empty path and successively applying operator/= for each element in the range [begin(), --end()).
Returns: empty() ? path() : *--end().
[ Example:
std::cout << path("/foo/bar.txt").filename(); // outputs "bar.txt"
std::cout << path("/").filename(); // outputs "/"
std::cout << path(".").filename(); // outputs "."
std::cout << path("..").filename(); // outputs ".."
— end example ]
Returns: if filename() contains a period but does not consist solely of one or two periods, returns the substring of filename() starting at its beginning and ending with the character before the last period. Otherwise, returns filename().
[ Example:
std::cout << path("/foo/bar.txt").stem(); // outputs "bar"
path p = "foo.bar.baz.tar";
for (; !p.extension().empty(); p = p.stem())
std::cout << p.extension() << '\n';
// outputs: .tar
// .baz
// .bar
— end example ]
Returns: if filename() contains a period but does not consist solely of one or two periods, returns the substring of filename() starting at the rightmost period and for the remainder of the path. Otherwise, returns an empty path object.
Remarks: Implementations are permitted to define additional behavior for file systems which append additional elements to extensions, such as alternate data streams or partitioned dataset names.
[ Example:
std::cout << path("/foo/bar.txt").extension(); // outputs ".txt"
— end example ]
[ Note: The period is included in the return value so that it is possible to distinguish between no extension and an empty extension. Also note that for a path p, p.stem()+p.extension() == p.filename(). — end note ]
Returns: pathstring.empty().
Returns: !root_path().empty().
Returns: !root_name().empty().
bool has_root_directory() const;
Returns: !root_directory().empty().
bool has_relative_path() const;
Returns: !relative_path().empty().
Returns: !parent_path().empty().
Returns: !filename().empty().
Returns: !stem().empty().
Returns: !extension().empty().
Returns: true if pathstring contains an absolute path ([fs.def.absolute.path]), else false.
[ Example: path("/").is_absolute() is true for POSIX-based operating systems, and false for Windows-based operating systems. — end example ]
Returns: !is_absolute().
path lexically_normal() const;
Returns: *this in normal form ([fs.def.normal.form]).
[ Example:
assert(path("foo/./bar/..").lexically_normal() == "foo");
assert(path("foo/.///bar/../").lexically_normal() == "foo/.");
The above assertions will succeed. The second example ends with a current directory (dot) element appended to support operating systems that use different syntax for directory names and regular file names.
On Windows, the returned path's directory-separator characters will be backslashes rather than slashes, but that does not affect path equality. — end example ]
path lexically_relative(const path& base) const;
Returns: *this made relative to base. Does not resolve ([fs.def.pathres]) symlinks. Does not first normalize ([fs.def.normal.form]) *this or base.
Effects: Determines the first mismatched element of *this and base as if by:
auto [a, b] = mismatch(begin(), end(), base.begin(), base.end());
Then,
if a == begin() and b == base.begin(), returns path(); otherwise
if a == end() and b == base.end(), returns path("."); otherwise
returns an object of class path that is default-constructed, followed by
application of operator/=(path("..")) for each element in [b, base.end()), and then
application of operator/= for each element in [a, end()).
[ Example:
assert(path("/a/d").lexically_relative("/a/b/c") == "../../d");
assert(path("/a/b/c").lexically_relative("/a/d") == "../b/c");
assert(path("a/b/c").lexically_relative("a") == "b/c");
assert(path("a/b/c").lexically_relative("a/b/c/x/y") == "../..");
assert(path("a/b/c").lexically_relative("a/b/c") == ".");
assert(path("a/b").lexically_relative("c/d") == "");
The above assertions will succeed. On Windows, the returned path's directory-separator characters will be backslashes rather than forward slashes, but that does not affect path equality. — end example ]
[ Note: If symlink following semantics are desired, use the operational function relative(). — end note ]
[ Note: If normalization ([fs.def.normal.form]) is needed to ensure consistent matching of elements, apply lexically_normal() to *this, base, or both. — end note ]
path lexically_proximate(const path& base) const;
Returns: If the value of lexically_relative(base) is not an empty path, return it. Otherwise return *this.
[ Note: If symlink following semantics are desired, use the operational function proximate(). — end note ]
[ Note: If normalization ([fs.def.normal.form]) is needed to ensure consistent matching of elements, apply lexically_normal() to *this, base, or both. — end note ]
Path iterators iterate over the elements of pathstring in the generic format ([path.generic]).
A path::iterator is a constant iterator satisfying all the requirements of a bidirectional iterator ([bidirectional.iterators]) except that, for dereferenceable iterators a and b of type path::iterator with a == b, there is no requirement that *a and *b are bound to the same object. Its value_type is path.
Calling any non-const member function of a path object invalidates all iterators referring to elements of that object.
For the elements of pathstring in the generic format, the forward traversal order is as follows:
The root-name element, if present.
The root-directory element, if present. [ Note: the generic format is required to ensure lexicographical comparison works correctly. — end note ]
Each successive filename element, if present.
dot, if one or more trailing non-root slash characters are present.
Returns: An iterator for the first present element in the traversal list above. If no elements are present, the end iterator.
Returns: The end iterator.
void swap(path& lhs, path& rhs) noexcept;
Effects: Equivalent to: lhs.swap(rhs);
size_t hash_value (const path& p) noexcept;
Returns: A hash value for the path p. If for two paths, p1 == p2 then hash_value(p1) == hash_value(p2).
bool operator< (const path& lhs, const path& rhs) noexcept;
Returns: lhs.compare(rhs) < 0.
bool operator<=(const path& lhs, const path& rhs) noexcept;
Returns: !(rhs < lhs).
bool operator> (const path& lhs, const path& rhs) noexcept;
Returns: rhs < lhs.
bool operator>=(const path& lhs, const path& rhs) noexcept;
Returns: !(lhs < rhs).
bool operator==(const path& lhs, const path& rhs) noexcept;
[ Note: Path equality and path equivalence have different semantics.
Equality is determined by the path non-member operator==, which considers the two path's lexical representations only. Thus path("foo") == "bar" is never true.
Equivalence is determined by the equivalent() non-member function, which determines if two paths resolve ([fs.def.pathres]) to the same file system entity. Thus equivalent("foo", "bar") will be true when both paths resolve to the same file.
Programmers wishing to determine if two paths are “the same” must decide if “the same” means “the same representation” or “resolve to the same actual file”, and choose the appropriate function accordingly. — end note ]
bool operator!=(const path& lhs, const path& rhs) noexcept;
Returns: !(lhs == rhs).
path operator/ (const path& lhs, const path& rhs);
Effects: Equivalent to: return path(lhs) /= rhs;
template <class charT, class traits>
basic_ostream<charT, traits>&
operator<<(basic_ostream<charT, traits>& os, const path& p);
Effects: Equivalent to: os << quoted(p.string<charT, traits>()); [ Note: The quoted function is described in [quoted.manip]. — end note ]
Returns: os.
template <class charT, class traits>
basic_istream<charT, traits>&
operator>>(basic_istream<charT, traits>& is, path& p);
Effects: Equivalent to:
basic_string<charT, traits> tmp; is >> quoted(tmp); p = tmp;
Returns: is.
template <class Source>
path u8path(const Source& source);
template <class InputIterator>
path u8path(InputIterator first, InputIterator last);
Requires: The source and [first, last) sequences are UTF-8 encoded. The value type of Source and InputIterator is char.
Returns:
If value_type is char and the current native narrow encoding ([fs.def.native.encode]) is UTF-8, return path(source) or path(first, last); otherwise,
if value_type is wchar_t and the native wide encoding is UTF-16, or if value_type is char16_t or char32_t, convert source or [first, last) to a temporary, tmp, of type string_type and return path(tmp); otherwise,
convert source or [first, last) to a temporary, tmp, of type u32string and return path(tmp).
Remarks: Argument format conversion ([path.fmt.cvt]) applies to the arguments for these functions. How Unicode encoding conversions are performed is unspecified.
[ Example: A string is to be read from a database that is encoded in UTF-8, and used to create a directory using the native encoding for filenames:
namespace fs = std::filesystem; std::string utf8_string = read_utf8_data(); fs::create_directory(fs::u8path(utf8_string));
For POSIX-based operating systems with the native narrow encoding set to UTF-8, no encoding or type conversion occurs.
For POSIX-based operating systems with the native narrow encoding not set to UTF-8, a conversion to UTF-32 occurs, followed by a conversion to the current native narrow encoding. Some Unicode characters may have no native character set representation.
For Windows-based operating systems a conversion from UTF-8 to UTF-16 occurs. — end example ]
namespace std::filesystem {
class filesystem_error : public system_error {
public:
filesystem_error(const string& what_arg, error_code ec);
filesystem_error(const string& what_arg,
const path& p1, error_code ec);
filesystem_error(const string& what_arg,
const path& p1, const path& p2, error_code ec);
const path& path1() const noexcept;
const path& path2() const noexcept;
const char* what() const noexcept override;
};
}
The class filesystem_error defines the type of objects thrown as exceptions to report file system errors from functions described in this subclause.
Constructors are provided that store zero, one, or two paths associated with an error.
Postconditions: The postconditions of this function are indicated in Table [tab:filesystem_error.1].
| Expression | Value |
| runtime_error::what() | what_arg.c_str() |
| code() | ec |
| path1().empty() | true |
| path2().empty() | true |
filesystem_error(const string& what_arg, const path& p1, error_code ec);
Postconditions: The postconditions of this function are indicated in Table [tab:filesystem_error.2].
| Expression | Value |
| runtime_error::what() | what_arg.c_str() |
| code() | ec |
| path1() | Reference to stored copy of p1 |
| path2().empty() | true |
filesystem_error(const string& what_arg, const path& p1, const path& p2, error_code ec);
Postconditions: The postconditions of this function are indicated in Table [tab:filesystem_error.3].
| Expression | Value |
| runtime_error::what() | what_arg.c_str() |
| code() | ec |
| path1() | Reference to stored copy of p1 |
| path2() | Reference to stored copy of p2 |
const path& path1() const noexcept;
Returns: A reference to the copy of p1 stored by the constructor, or, if none, an empty path.
const path& path2() const noexcept;
Returns: A reference to the copy of p2 stored by the constructor, or, if none, an empty path.
const char* what() const noexcept override;
Returns: A string containing runtime_error::what(). The exact format is unspecified. Implementations are encouraged but not required to include path1.native_string() if not empty, path2.native_string() if not empty, and system_error::what() strings in the returned string.
This enum class specifies constants used to identify file types, with the meanings listed in Table [tab:enum.file_type].
The enum class type copy_options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to control the semantics of copy operations. The constants are specified in option groups with the meanings listed in Table [tab:enum.copy_options]. Constant none is shown in each option group for purposes of exposition; implementations shall provide only a single definition. Calling a library function with more than a single constant for an option group results in undefined behavior.
| Option group controlling copy_file function effects for existing target files | |
| Constant | Meaning |
| none | (Default) Error; file already exists. |
| skip_existing | Do not overwrite existing file, do not report an error. |
| overwrite_existing | Overwrite the existing file. |
| update_existing | Overwrite the existing file if it is older than the replacement file. |
| Option group controlling copy function effects for sub-directories | |
| Constant | Meaning |
| none | (Default) Do not copy sub-directories. |
| recursive | Recursively copy sub-directories and their contents. |
| Option group controlling copy function effects for symbolic links | |
| Constant | Meaning |
| none | (Default) Follow symbolic links. |
| copy_symlinks | Copy symbolic links as symbolic links rather than copying the files that they point to. |
| skip_symlinks | Ignore symbolic links. |
| Option group controlling copy function effects for choosing the form of copying | |
| Constant | Meaning |
| none | (Default) Copy content. |
| directories_only | Copy directory structure only, do not copy non-directory files. |
| create_symlinks | Make symbolic links instead of copies of files. The source path shall be an absolute path unless the destination path is in the current directory. |
| create_hard_links | Make hard links instead of copies of files. |
The enum class type perms is a bitmask type ([bitmask.types]) that specifies bitmask constants used to identify file permissions, with the meanings listed in Table [tab:enum.perms].
| Name | Value | POSIX | Definition or notes |
| (octal) | macro | ||
| none | 0 | There are no permissions set for the file. | |
| owner_read | 0400 | S_IRUSR | Read permission, owner |
| owner_write | 0200 | S_IWUSR | Write permission, owner |
| owner_exec | 0100 | S_IXUSR | Execute/search permission, owner |
| owner_all | 0700 | S_IRWXU |
Read, write, execute/search by owner; owner_read | owner_write | owner_exec |
| group_read | 040 | S_IRGRP | Read permission, group |
| group_write | 020 | S_IWGRP | Write permission, group |
| group_exec | 010 | S_IXGRP | Execute/search permission, group |
| group_all | 070 | S_IRWXG |
Read, write, execute/search by group; group_read | group_write | group_exec |
| others_read | 04 | S_IROTH | Read permission, others |
| others_write | 02 | S_IWOTH | Write permission, others |
| others_exec | 01 | S_IXOTH | Execute/search permission, others |
| others_all | 07 | S_IRWXO |
Read, write, execute/search by others; others_read | others_write | others_exec |
| all | 0777 | owner_all | group_all | others_all | |
| set_uid | 04000 | S_ISUID | Set-user-ID on execution |
| set_gid | 02000 | S_ISGID | Set-group-ID on execution |
| sticky_bit | 01000 | S_ISVTX | Operating system dependent. |
| mask | 07777 | all | set_uid | set_gid | sticky_bit | |
| unknown | 0xFFFF | The permissions are not known, such as when a file_status object is created without specifying the permissions | |
| add_perms | 0x10000 | permissions() shall bitwise or the perm argument's permission bits to the file's current permission bits. | |
| remove_perms | 0x20000 | permissions() shall bitwise and the complement of perm argument's permission bits to the file's current permission bits. | |
| symlink_nofollow | 0x40000 | permissions() shall change the permissions of symbolic links. |
The enum class type directory_options is a bitmask type ([bitmask.types]) that specifies bitmask constants used to identify directory traversal options, with the meanings listed in Table [tab:enum.directory_options].
| Name | Meaning |
| none | (Default) Skip directory symlinks, permission denied is an error. |
| follow_directory_symlink | Follow rather than skip directory symlinks. |
| skip_permission_denied | Skip directories that would otherwise result in permission denied. |
namespace std::filesystem {
class file_status {
public:
// [file_status.cons], constructors and destructor
explicit file_status(file_type ft = file_type::none,
perms prms = perms::unknown) noexcept;
file_status(const file_status&) noexcept = default;
file_status(file_status&&) noexcept = default;
~file_status();
// assignments:
file_status& operator=(const file_status&) noexcept = default;
file_status& operator=(file_status&&) noexcept = default;
// [file_status.mods], modifiers
void type(file_type ft) noexcept;
void permissions(perms prms) noexcept;
// [file_status.obs], observers
file_type type() const noexcept;
perms permissions() const noexcept;
};
}
An object of type file_status stores information about the type and permissions of a file.
explicit file_status() noexcept;
Postconditions: type() == file_type::none and permissions() == perms::unknown.
explicit file_status(file_type ft, perms prms = perms::unknown) noexcept;
Postconditions: type() == ft and permissions() == prms.
file_type type() const noexcept;
Returns: The value of type() specified by the postconditions of the most recent call to a constructor, operator=, or type(file_type) function.
perms permissions() const noexcept;
Returns: The value of permissions() specified by the postconditions of the most recent call to a constructor, operator=, or permissions(perms) function.
void type(file_type ft) noexcept;
Postconditions: type() == ft.
void permissions(perms prms) noexcept;
Postconditions: permissions() == prms.
namespace std::filesystem {
class directory_entry {
public:
// [directory_entry.cons], constructors and destructor
explicit directory_entry(const path& p);
directory_entry() noexcept = default;
directory_entry(const directory_entry&) = default;
directory_entry(directory_entry&&) noexcept = default;
~directory_entry();
// assignments:
directory_entry& operator=(const directory_entry&) = default;
directory_entry& operator=(directory_entry&&) noexcept = default;
// [directory_entry.mods], modifiers
void assign(const path& p);
void replace_filename(const path& p);
// [directory_entry.obs], observers
const path& path() const noexcept;
operator const path&() const noexcept;
file_status status() const;
file_status status(error_code& ec) const noexcept;
file_status symlink_status() const;
file_status symlink_status(error_code& ec) const noexcept;
bool operator< (const directory_entry& rhs) const noexcept;
bool operator==(const directory_entry& rhs) const noexcept;
bool operator!=(const directory_entry& rhs) const noexcept;
bool operator<=(const directory_entry& rhs) const noexcept;
bool operator> (const directory_entry& rhs) const noexcept;
bool operator>=(const directory_entry& rhs) const noexcept;
private:
path pathobject; // exposition only
};
}
A directory_entry object stores a path object.
explicit directory_entry(const path& p);
Effects: Constructs an object of type directory_entry.
Postconditions: path() == p.
Postconditions: path() == p.
void replace_filename(const path& p);
Postconditions: path() == x.parent_path() / p where x is the value of path() before the function is called.
const path& path() const noexcept;
operator const path&() const noexcept;
Returns: pathobject.
file_status status() const;
file_status status(error_code& ec) const noexcept;
Returns: status(path()) or status(path(), ec), respectively.
Throws: As specified in [fs.err.report].
file_status symlink_status() const;
file_status symlink_status(error_code& ec) const noexcept;
Returns: symlink_status(path()) or symlink_status(path(), ec), respectively.
Throws: As specified in [fs.err.report].
bool operator==(const directory_entry& rhs) const noexcept;
Returns: pathobject == rhs.pathobject.
bool operator!=(const directory_entry& rhs) const noexcept;
Returns: pathobject != rhs.pathobject.
bool operator< (const directory_entry& rhs) const noexcept;
Returns: pathobject < rhs.pathobject.
bool operator<=(const directory_entry& rhs) const noexcept;
Returns: pathobject <= rhs.pathobject.
bool operator> (const directory_entry& rhs) const noexcept;
Returns: pathobject > rhs.pathobject.
bool operator>=(const directory_entry& rhs) const noexcept;
Returns: pathobject >= rhs.pathobject.
An object of type directory_iterator provides an iterator for a sequence of directory_entry elements representing the files in a directory. [ Note: For iteration into sub-directories, see class recursive_directory_iterator ([class.rec.dir.itr]). — end note ]
namespace std::filesystem {
class directory_iterator {
public:
using iterator_category = input_iterator_tag;
using value_type = directory_entry;
using difference_type = ptrdiff_t;
using pointer = const directory_entry*;
using reference = const directory_entry&;
// [directory_iterator.members], member functions
directory_iterator() noexcept;
explicit directory_iterator(const path& p);
directory_iterator(const path& p, directory_options options);
directory_iterator(const path& p, error_code& ec) noexcept;
directory_iterator(const path& p, directory_options options,
error_code& ec) noexcept;
directory_iterator(const directory_iterator& rhs);
directory_iterator(directory_iterator&& rhs) noexcept;
~directory_iterator();
directory_iterator& operator=(const directory_iterator& rhs);
directory_iterator& operator=(directory_iterator&& rhs) noexcept;
const directory_entry& operator*() const;
const directory_entry* operator->() const;
directory_iterator& operator++();
directory_iterator& increment(error_code& ec) noexcept;
// other members as required by [input.iterators], input iterators
};
}
directory_iterator satisfies the requirements of an input iterator ([input.iterators]).
If an iterator of type directory_iterator reports an error or is advanced past the last directory element, that iterator shall become equal to the end iterator value. The directory_iterator default constructor shall create an iterator equal to the end iterator value, and this shall be the only valid iterator for the end condition.
The end iterator is not dereferenceable.
Two end iterators are always equal. An end iterator shall not be equal to a non-end iterator.
The result of calling the path() member of the directory_entry object obtained by dereferencing a directory_iterator is a reference to a path object composed of the directory argument from which the iterator was constructed with filename of the directory entry appended as if by operator/=.
Directory iteration shall not yield directory entries for the current (dot) and parent (dot-dot) directories.
The order of directory entries obtained by dereferencing successive increments of a directory_iterator is unspecified.
[ Note: Programs performing directory iteration may wish to test if the path obtained by dereferencing a directory iterator actually exists. It could be a symbolic link to a non-existent file. Programs recursively walking directory trees for purposes of removing and renaming entries may wish to avoid following symbolic links.
If a file is removed from or added to a directory after the construction of a directory_iterator for the directory, it is unspecified whether or not subsequently incrementing the iterator will ever result in an iterator referencing the removed or added directory entry. See POSIX readdir_r. — end note ]
directory_iterator() noexcept;
Effects: Constructs the end iterator.
explicit directory_iterator(const path& p);
directory_iterator(const path& p, directory_options options);
directory_iterator(const path& p, error_code& ec) noexcept;
directory_iterator(const path& p, directory_options options, error_code& ec) noexcept;
Effects: For the directory that p resolves to, constructs an iterator for the first element in a sequence of directory_entry elements representing the files in the directory, if any; otherwise the end iterator. However, if
(options & directory_options::skip_permission_denied) != directory_options::none
and construction encounters an error indicating that permission to access p is denied, constructs the end iterator and does not report an error.
Throws: As specified in [fs.err.report].
[ Note: To iterate over the current directory, use directory_iterator(".") rather than directory_iterator(""). — end note ]
directory_iterator(const directory_iterator& rhs);
directory_iterator(directory_iterator&& rhs) noexcept;
Effects: Constructs an object of class directory_iterator.
Postconditions: *this has the original value of rhs.
directory_iterator& operator=(const directory_iterator& rhs);
directory_iterator& operator=(directory_iterator&& rhs) noexcept;
Effects: If *this and rhs are the same object, the member has no effect.
Postconditions: *this has the original value of rhs.
Returns: *this.
directory_iterator& operator++();
directory_iterator& increment(error_code& ec) noexcept;
Effects: As specified for the prefix increment operation of Input iterators ([input.iterators]).
Returns: *this.
Throws: As specified in [fs.err.report].
These functions enable range access for directory_iterator.
Returns: iter.
directory_iterator end(const directory_iterator&) noexcept;
Returns: directory_iterator().
An object of type recursive_directory_iterator provides an iterator for a sequence of directory_entry elements representing the files in a directory and its sub-directories.
namespace std::filesystem {
class recursive_directory_iterator {
public:
using iterator_category = input_iterator_tag;
using value_type = directory_entry;
using difference_type = ptrdiff_t;
using pointer = const directory_entry*;
using reference = const directory_entry&;
// [rec.dir.itr.members], constructors and destructor
recursive_directory_iterator() noexcept;
explicit recursive_directory_iterator(const path& p);
recursive_directory_iterator(const path& p, directory_options options);
recursive_directory_iterator(const path& p, directory_options options,
error_code& ec) noexcept;
recursive_directory_iterator(const path& p, error_code& ec) noexcept;
recursive_directory_iterator(const recursive_directory_iterator& rhs);
recursive_directory_iterator(recursive_directory_iterator&& rhs) noexcept;
~recursive_directory_iterator();
// [rec.dir.itr.members], observers
directory_options options() const;
int depth() const;
bool recursion_pending() const;
const directory_entry& operator*() const;
const directory_entry* operator->() const;
// [rec.dir.itr.members], modifiers
recursive_directory_iterator&
operator=(const recursive_directory_iterator& rhs);
recursive_directory_iterator&
operator=(recursive_directory_iterator&& rhs) noexcept;
recursive_directory_iterator& operator++();
recursive_directory_iterator& increment(error_code& ec) noexcept;
void pop();
void pop(error_code& ec);
void disable_recursion_pending();
// other members as required by [input.iterators], input iterators
};
}
Calling options, depth, recursion_pending, pop or disable_recursion_pending on an iterator that is not dereferenceable results in undefined behavior.
The behavior of a recursive_directory_iterator is the same as a directory_iterator unless otherwise specified.
[ Note: If the directory structure being iterated over contains cycles then the end iterator may be unreachable. — end note ]
recursive_directory_iterator() noexcept;
Effects: Constructs the end iterator.
explicit recursive_directory_iterator(const path& p);
recursive_directory_iterator(const path& p, directory_options options);
recursive_directory_iterator(const path& p, directory_options options, error_code& ec) noexcept;
recursive_directory_iterator(const path& p, error_code& ec) noexcept;
Effects: Constructs a iterator representing the first entry in the directory p resolves to, if any; otherwise, the end iterator. However, if
(options & directory_options::skip_permission_denied) != directory_options::none
and construction encounters an error indicating that permission to access p is denied, constructs the end iterator and does not report an error.
Postconditions: options() == options for the signatures with a directory_options argument, otherwise options() == directory_options::none.
Throws: As specified in [fs.err.report].
[ Note: To iterate over the current directory, use recursive_directory_iterator(".") rather than recursive_directory_iterator(""). — end note ]
[ Note: By default, recursive_directory_iterator does not follow directory symlinks. To follow directory symlinks, specify options as directory_options::follow_directory_symlink — end note ]
recursive_directory_iterator(const recursive_directory_iterator& rhs);
Effects: Constructs an object of class recursive_directory_iterator.
recursive_directory_iterator(recursive_directory_iterator&& rhs) noexcept;
Effects: Constructs an object of class recursive_directory_iterator.
Postconditions: options(), depth(), and recursion_pending() return the values that rhs.options(), rhs.depth(), and rhs.recursion_pending(), respectively, had before the function call.
recursive_directory_iterator& operator=(const recursive_directory_iterator& rhs);
Effects: If *this and rhs are the same object, the member has no effect.
Returns: *this.
recursive_directory_iterator& operator=(recursive_directory_iterator&& rhs) noexcept;
Effects: If *this and rhs are the same object, the member has no effect.
Postconditions: options(), depth(), and recursion_pending() return the values that rhs.options(), rhs.depth(), and rhs.recursion_pending(), respectively, had before the function call.
Returns: *this.
directory_options options() const;
Returns: The value of the constructor options argument, if present, otherwise directory_options::none.
Throws: Nothing.
Returns: The current depth of the directory tree being traversed. [ Note: The initial directory is depth 0, its immediate subdirectories are depth 1, and so forth. — end note ]
Throws: Nothing.
bool recursion_pending() const;
Returns: true if disable_recursion_pending() has not been called subsequent to the prior construction or increment operation, otherwise false.
Throws: Nothing.
recursive_directory_iterator& operator++();
recursive_directory_iterator& increment(error_code& ec) noexcept;
Effects: As specified for the prefix increment operation of Input iterators ([input.iterators]), except that:
If there are no more entries at the current depth, then if depth()!= 0 iteration over the parent directory resumes; otherwise *this = recursive_directory_iterator().
Otherwise if
recursion_pending() && is_directory((*this)->status()) && (!is_symlink((*this)->symlink_status()) || (options() & directory_options::follow_directory_symlink) != directory_options::none)
then either directory (*this)->path() is recursively iterated into or, if
(options() & directory_options::skip_permission_denied) != directory_options::none
and an error occurs indicating that permission to access directory (*this)->path() is denied, then directory (*this)->path() is treated as an empty directory and no error is reported.
Returns: *this.
Throws: As specified in [fs.err.report].
void pop();
void pop(error_code& ec);
Effects: If depth() == 0, set *this to recursive_directory_iterator(). Otherwise, cease iteration of the directory currently being iterated over, and continue iteration over the parent directory.
Throws: As specified in [fs.err.report].
void disable_recursion_pending();
Postconditions: recursion_pending() == false.
[ Note: disable_recursion_pending() is used to prevent unwanted recursion into a directory. — end note ]
These functions enable use of recursive_directory_iterator with range-based for statements.
recursive_directory_iterator begin(recursive_directory_iterator iter) noexcept;
Returns: iter.
recursive_directory_iterator end(const recursive_directory_iterator&) noexcept;
Returns: recursive_directory_iterator().
Filesystem operation functions query or modify files, including directories, in external storage.
[ Note: Because hardware failures, network failures, file system races ([fs.def.race]), and many other kinds of errors occur frequently in file system operations, users should be aware that any filesystem operation function, no matter how apparently innocuous, may encounter an error; see [fs.err.report]. — end note ]
path absolute(const path& p, const path& base = current_path());
Returns: An absolute path ([fs.def.absolute.path]) composed according to Table [tab:absolute.path].
| p.has_root_directory() | !p.has_root_directory() | |
| p.has_root_name() | p |
2.4in
p.root_name() / absolute(base).root_directory() / absolute(base).relative_path() / p.relative_path() |
| !p.has_root_name() | absolute(base).root_name() / p | absolute(base) / p |
[ Note: For the returned path, rp, rp.is_absolute() is true. — end note ]
Throws: As specified in [fs.err.report].
path canonical(const path& p, const path& base = current_path());
path canonical(const path& p, error_code& ec);
path canonical(const path& p, const path& base, error_code& ec);
Effects: Converts p, which must exist, to an absolute path that has no symbolic link, ".", or ".." elements.
Returns: A path that refers to the same file system object as absolute(p, base). For the overload without a base argument, base is current_path(). Signatures with argument ec return path() if an error occurs.
Throws: As specified in [fs.err.report].
Remarks: !exists(p) is an error.
void copy(const path& from, const path& to);
void copy(const path& from, const path& to, error_code& ec) noexcept;
Effects: Equivalent to copy(from, to, copy_options::none) or copy(from, to, copy_options::none, ec), respectively.
void copy(const path& from, const path& to, copy_options options);
void copy(const path& from, const path& to, copy_options options,
error_code& ec) noexcept;
Requires: At most one constant from each option group ([enum.copy_options]) is present in options.
Effects: Before the first use of f and t:
If
(options & copy_options::create_symlinks) != copy_options::none || (options & copy_options::skip_symlinks) != copy_options::none
then auto f = symlink_status(from) and if needed auto t = symlink_status(to).
Otherwise, if
(options & copy_options::copy_symlinks) != copy_options::none
then auto f = symlink_status(from) and if needed auto t = status(to).
Otherwise, auto f = status(from) and if needed auto t = status(to).
Effects are then as follows:
An error is reported as specified in [fs.err.report] if:
!exists(f), or
equivalent(from, to), or
is_other(f) || is_other(t), or
is_directory(f) && is_regular_file(t).
Otherwise, if is_symlink(f), then:
If (options & copy_options::skip_symlinks) != copy_options::none then return.
Otherwise if
!exists(t) && (options & copy_options::copy_symlinks) != copy_options::none
then copy_symlink(from, to).
Otherwise report an error as specified in [fs.err.report].
Otherwise, if is_regular_file(f), then:
If (options & copy_options::directories_only) != copy_options::none, then return.
Otherwise if (options & copy_options::create_symlinks) != copy_options::none, then create a symbolic link to the source file.
Otherwise if (options & copy_options::create_hard_links) != copy_options::none, then create a hard link to the source file.
Otherwise if is_directory(t), then copy_file(from, to/from.filename(), options).
Otherwise, copy_file(from, to, options).
Otherwise, if
is_directory(f) && ((options & copy_options::recursive) != copy_options::none || options == copy_options::none)
then:
If !exists(t), then create_directory(to, from).
Then, iterate over the files in from, as if by for (const directory_entry& x : directory_iterator(from)), and for each iteration
copy(x.path(), to/x.path().filename(), options | copy_options::unspecified)
Otherwise, for the signature with argument ec, ec.clear().
Otherwise, no effects.
Throws: As specified in [fs.err.report].
Remarks: For the signature with argument ec, any library functions called by the implementation shall have an error_code argument if applicable.
[ Example: Given this directory structure:
/dir1
file1
file2
dir2
file3
Calling copy("/dir1", "/dir3") would result in:
/dir1
file1
file2
dir2
file3
/dir3
file1
file2
Alternatively, calling copy("/dir1", "/dir3", copy_options::recursive) would result in:
/dir1
file1
file2
dir2
file3
/dir3
file1
file2
dir2
file3
— end example ]
bool copy_file(const path& from, const path& to);
bool copy_file(const path& from, const path& to, error_code& ec) noexcept;
Returns: copy_file(from, to, copy_options::none) or
copy_file(from, to, copy_options::none, ec), respectively.
Throws: As specified in [fs.err.report].
bool copy_file(const path& from, const path& to, copy_options options);
bool copy_file(const path& from, const path& to, copy_options options,
error_code& ec) noexcept;
Requires: At most one constant from each copy_options option group ([enum.copy_options]) is present in options.
Effects: As follows:
Report a file already exists error as specified in [fs.err.report] if:
!is_regular_file(from), or
exists(to) and !is_regular_file(to), or
exists(to) and equivalent(from, to), or
exists(to) and (options & (copy_options::skip_existing | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none.
Otherwise, copy the contents and attributes of the file from resolves to, to the file to resolves to, if:
!exists(to), or
exists(to) and (options & copy_options::overwrite_existing) != copy_options::none, or
exists(to) and (options & copy_options::update_existing) != copy_options::none and from is more recent than to, determined as if by use of the last_write_time function ([fs.op.last_write_time]).
Otherwise, no effects.
Returns: true if the from file was copied, otherwise false. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
Complexity: At most one direct or indirect invocation of status(to).
void copy_symlink(const path& existing_symlink, const path& new_symlink);
void copy_symlink(const path& existing_symlink, const path& new_symlink,
error_code& ec) noexcept;
Effects: Equivalent to
function(read_symlink(existing_symlink), new_symlink) or
function(read_symlink(existing_symlink, ec), new_symlink, ec), respectively,
where function is create_symlink or
create_directory_symlink, as appropriate.
Throws: As specified in [fs.err.report].
bool create_directories(const path& p);
bool create_directories(const path& p, error_code& ec) noexcept;
Effects: Establishes the postcondition by calling create_directory() for any element of p that does not exist.
Postconditions: is_directory(p).
Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
Complexity: Ο(n) where n is the number of elements of p that do not exist.
bool create_directory(const path& p);
bool create_directory(const path& p, error_code& ec) noexcept;
Effects: Establishes the postcondition by attempting to create the directory p resolves to, as if by POSIX mkdir() with a second argument of static_cast<int>(perms::all). Creation failure because p resolves to an existing directory shall not be treated as an error.
Postconditions: is_directory(p).
Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool create_directory(const path& p, const path& existing_p);
bool create_directory(const path& p, const path& existing_p, error_code& ec) noexcept;
Effects: Establishes the postcondition by attempting to create the directory p resolves to, with attributes copied from directory existing_p. The set of attributes copied is operating system dependent. Creation failure because p resolves to an existing directory shall not be treated as an error. [ Note: For POSIX-based operating systems, the attributes are those copied by native API stat(existing_p.c_str(), &attributes_stat) followed by mkdir(p.c_str(), attributes_stat.st_mode). For Windows-based operating systems, the attributes are those copied by native API CreateDirectoryExW(existing_p.c_str(), p.c_str(), 0). — end note ]
Postconditions: is_directory(p).
Returns: true if a new directory was created, otherwise false. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
void create_directory_symlink(const path& to, const path& new_symlink);
void create_directory_symlink(const path& to, const path& new_symlink,
error_code& ec) noexcept;
Effects: Establishes the postcondition, as if by POSIX symlink().
Postconditions: new_symlink resolves to a symbolic link file that contains an unspecified representation of to.
Throws: As specified in [fs.err.report].
[ Note: Some operating systems require symlink creation to identify that the link is to a directory. Portable code should use create_directory_symlink() to create directory symlinks rather than create_symlink() — end note ]
[ Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support symbolic links regardless of the operating system. — end note ]
void create_hard_link(const path& to, const path& new_hard_link);
void create_hard_link(const path& to, const path& new_hard_link,
error_code& ec) noexcept;
Effects: Establishes the postcondition, as if by POSIX link().
Throws: As specified in [fs.err.report].
[ Note: Some operating systems do not support hard links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support hard links regardless of the operating system. Some file systems limit the number of links per file. — end note ]
void create_symlink(const path& to, const path& new_symlink);
void create_symlink(const path& to, const path& new_symlink,
error_code& ec) noexcept;
Effects: Establishes the postcondition, as if by POSIX symlink().
Postconditions: new_symlink resolves to a symbolic link file that contains an unspecified representation of to.
Throws: As specified in [fs.err.report].
[ Note: Some operating systems do not support symbolic links at all or support them only for regular files. Some file systems (such as the FAT file system) do not support symbolic links regardless of the operating system. — end note ]
path current_path();
path current_path(error_code& ec);
Returns: The absolute path of the current working directory, obtained as if by POSIX getcwd(). The signature with argument ec returns path() if an error occurs.
Throws: As specified in [fs.err.report].
Remarks: The current working directory is the directory, associated with the process, that is used as the starting location in pathname resolution for relative paths.
[ Note: The current_path() name was chosen to emphasize that the returned value is a path, not just a single directory name.
The current path as returned by many operating systems is a dangerous global variable. It may be changed unexpectedly by a third-party or system library functions, or by another thread. — end note ]
void current_path(const path& p);
void current_path(const path& p, error_code& ec) noexcept;
Effects: Establishes the postcondition, as if by POSIX chdir().
Postconditions: equivalent(p, current_path()).
Throws: As specified in [fs.err.report].
[ Note: The current path for many operating systems is a dangerous global state. It may be changed unexpectedly by a third-party or system library functions, or by another thread. — end note ]
bool equivalent(const path& p1, const path& p2);
bool equivalent(const path& p1, const path& p2, error_code& ec) noexcept;
Let s1 and s2 be file_statuss, determined as if by status(p1) and status(p2), respectively.
Effects: Determines s1 and s2. If (!exists(s1) && !exists(s2)) || (is_other(s1) && is_other(s2)) an error is reported ([fs.err.report]).
Returns: true, if s1 == s2 and p1 and p2 resolve to the same file system entity, else false. The signature with argument ec returns false if an error occurs.
Two paths are considered to resolve to the same file system entity if two candidate entities reside on the same device at the same location. This is determined as if by the values of the POSIX stat structure, obtained as if by stat() for the two paths, having equal st_dev values and equal st_ino values.
Throws: As specified in ([fs.err.report]).
bool exists(file_status s) noexcept;
Returns: status_known(s) && s.type() != file_type::not_found.
bool exists(const path& p);
bool exists(const path& p, error_code& ec) noexcept;
Let s be a file_status, determined as if by status(p) or status(p, ec), respectively.
Effects: The signature with argument ec calls ec.clear() if status_known(s).
Returns: exists(s).
Throws: As specified in [fs.err.report].
uintmax_t file_size(const path& p);
uintmax_t file_size(const path& p, error_code& ec) noexcept;
Returns: If !exists(p) || !is_regular_file(p) an error is reported ([fs.err.report]). Otherwise, the size in bytes of the file p resolves to, determined as if by the value of the POSIX stat structure member st_size obtained as if by POSIX stat(). The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.
Throws: As specified in [fs.err.report].
uintmax_t hard_link_count(const path& p);
uintmax_t hard_link_count(const path& p, error_code& ec) noexcept;
Returns: The number of hard links for p. The signature with argument ec returns static_cast<uintmax_t>(-1) if an error occurs.
Throws: As specified in [fs.err.report].
bool is_block_file(file_status s) noexcept;
Returns: s.type() == file_type::block.
bool is_block_file(const path& p);
bool is_block_file(const path& p, error_code& ec) noexcept;
Returns: is_block_file(status(p)) or is_block_file(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_character_file(file_status s) noexcept;
Returns: s.type() == file_type::character.
bool is_character_file(const path& p);
bool is_character_file(const path& p, error_code& ec) noexcept;
Returns: is_character_file(status(p)) or is_character_file(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_directory(file_status s) noexcept;
Returns: s.type() == file_type::directory.
bool is_directory(const path& p);
bool is_directory(const path& p, error_code& ec) noexcept;
Returns: is_directory(status(p)) or is_directory(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_empty(const path& p);
bool is_empty(const path& p, error_code& ec) noexcept;
Effects:
Determine file_status s, as if by status(p) or status(p, ec), respectively.
For the signature with argument ec, return false if an error occurred.
Otherwise, if is_directory(s):
Create directory_iterator itr, as if by directory_iterator(p) or directory_iterator(p, ec), respectively.
For the signature with argument ec, return false if an error occurred.
Otherwise, return itr == directory_iterator().
Otherwise:
Determine uintmax_t sz, as if by file_size(p) or file_size(p, ec), respectively.
For the signature with argument ec, return false if an error occurred.
Otherwise, return sz == 0.
Throws: As specified in [fs.err.report].
bool is_fifo(file_status s) noexcept;
Returns: s.type() == file_type::fifo.
bool is_fifo(const path& p);
bool is_fifo(const path& p, error_code& ec) noexcept;
Returns: is_fifo(status(p)) or is_fifo(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_other(file_status s) noexcept;
Returns: exists(s) && !is_regular_file(s) && !is_directory(s) && !is_symlink(s).
bool is_other(const path& p);
bool is_other(const path& p, error_code& ec) noexcept;
Returns: is_other(status(p)) or is_other(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_regular_file(file_status s) noexcept;
Returns: s.type() == file_type::regular.
bool is_regular_file(const path& p);
Returns: is_regular_file(status(p)).
Throws: filesystem_error if status(p) would throw filesystem_error.
bool is_regular_file(const path& p, error_code& ec) noexcept;
Effects: Sets ec as if by status(p, ec). [ Note: file_type::none, file_type::not_found and file_type::unknown cases set ec to error values. To distinguish between cases, call the status function directly. — end note ]
Returns: is_regular_file(status(p, ec)). Returns false if an error occurs.
bool is_socket(file_status s) noexcept;
Returns: s.type() == file_type::socket.
bool is_socket(const path& p);
bool is_socket(const path& p, error_code& ec) noexcept;
Returns: is_socket(status(p)) or is_socket(status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
bool is_symlink(file_status s) noexcept;
Returns: s.type() == file_type::symlink.
bool is_symlink(const path& p);
bool is_symlink(const path& p, error_code& ec) noexcept;
Returns: is_symlink(symlink_status(p)) or is_symlink(symlink_status(p, ec)), respectively. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
file_time_type last_write_time(const path& p);
file_time_type last_write_time(const path& p, error_code& ec) noexcept;
Returns: The time of last data modification of p, determined as if by the value of the POSIX stat structure member st_mtime obtained as if by POSIX stat(). The signature with argument ec returns file_time_type::min() if an error occurs.
Throws: As specified in [fs.err.report].
void last_write_time(const path& p, file_time_type new_time);
void last_write_time(const path& p, file_time_type new_time,
error_code& ec) noexcept;
Effects: Sets the time of last data modification of the file resolved to by p to new_time, as if by POSIX futimens().
Throws: As specified in [fs.err.report].
[ Note: A postcondition of last_write_time(p) == new_time is not specified since it might not hold for file systems with coarse time granularity. — end note ]
void permissions(const path& p, perms prms);
void permissions(const path& p, perms prms, error_code& ec);
Requires: !((prms & perms::add_perms) != perms::none && (prms & perms::remove_perms) != perms::none).
Effects: Applies the effective permissions bits from prms to the file p resolves to, or if that file is a symbolic link and symlink_nofollow is not set in prms, the file that it points to, as if by POSIX fchmodat(). The effective permission bits are determined as specified in Table [tab:fs.op.permissions], where s is the result of (prms & perms::symlink_nofollow) != perms::none ? symlink_status(p) : status(p).
| Bits present in prms | Effective bits applied |
| Neither add_perms nor remove_perms | prms & perms::mask |
| add_perms | s.permissions() | (prms & perms::mask) |
| remove_perms | s.permissions() & ~(prms & perms::mask) |
[ Note: Conceptually permissions are viewed as bits, but the actual implementation may use some other mechanism. — end note ]
Throws: As specified in [fs.err.report].
path proximate(const path& p, error_code& ec);
Returns: proximate(p, current_path(), ec).
Throws: As specified in [fs.err.report].
path proximate(const path& p, const path& base = current_path());
path proximate(const path& p, const path& base, error_code& ec);
Returns: For the first form:
weakly_canonical(p).lexically_proximate(weakly_canonical(base));
For the second form:
weakly_canonical(p, ec).lexically_proximate(weakly_canonical(base, ec));
or path() at the first error occurrence, if any.
Throws: As specified in [fs.err.report].
path read_symlink(const path& p);
path read_symlink(const path& p, error_code& ec);
Returns: If p resolves to a symbolic link, a path object containing the contents of that symbolic link. The signature with argument ec returns path() if an error occurs.
Throws: As specified in [fs.err.report]. [ Note: It is an error if p does not resolve to a symbolic link. — end note ]
path relative(const path& p, error_code& ec);
Returns: relative(p, current_path(), ec).
Throws: As specified in [fs.err.report].
path relative(const path& p, const path& base = current_path());
path relative(const path& p, const path& base, error_code& ec);
Returns: For the first form:
weakly_canonical(p).lexically_relative(weakly_canonical(base));
For the second form:
weakly_canonical(p, ec).lexically_relative(weakly_canonical(base, ec));
or path() at the first error occurrence, if any.
Throws: As specified in [fs.err.report].
bool remove(const path& p);
bool remove(const path& p, error_code& ec) noexcept;
Effects: If exists(symlink_status(p, ec)), the file p is removed as if by POSIX remove(). [ Note: A symbolic link is itself removed, rather than the file it resolves to. — end note ]
Postconditions: !exists(symlink_status(p)).
Returns: false if p did not exist, otherwise true. The signature with argument ec returns false if an error occurs.
Throws: As specified in [fs.err.report].
uintmax_t remove_all(const path& p);
uintmax_t remove_all(const path& p, error_code& ec) noexcept;
Effects: Recursively deletes the contents of p if it exists, then deletes file p itself, as if by POSIX remove(). [ Note: A symbolic link is itself removed, rather than the file it resolves to. — end note ]
Postconditions: !exists(symlink_status(p)).
Returns: The number of files removed. The signature with argument ec returns static_cast< uintmax_t>(-1) if an error occurs.
Throws: As specified in [fs.err.report].
void rename(const path& old_p, const path& new_p);
void rename(const path& old_p, const path& new_p, error_code& ec) noexcept;
Effects: Renames old_p to new_p, as if by POSIX rename().
[ Note:
If old_p and new_p resolve to the same existing file, no action is taken.
Otherwise, the rename may include the following effects:
if new_p resolves to an existing non-directory file, new_p is removed; otherwise,
if new_p resolves to an existing directory, new_p is removed if empty on POSIX compliant operating systems but may be an error on other operating systems.
A symbolic link is itself renamed, rather than the file it resolves to. — end note ]
Throws: As specified in [fs.err.report].
void resize_file(const path& p, uintmax_t new_size);
void resize_file(const path& p, uintmax_t new_size, error_code& ec) noexcept;
Postconditions: file_size(p) == new_size.
Throws: As specified in [fs.err.report].
Remarks: Achieves its postconditions as if by POSIX truncate().
space_info space(const path& p);
space_info space(const path& p, error_code& ec) noexcept;
Returns: An object of type space_info. The value of the space_info object is determined as if by using POSIX statvfs to obtain a POSIX struct statvfs, and then multiplying its f_blocks, f_bfree, and f_bavail members by its f_frsize member, and assigning the results to the capacity, free, and available members respectively. Any members for which the value cannot be determined shall be set to static_cast<uintmax_t>(-1). For the signature with argument ec, all members are set to static_cast<uintmax_t>(-1) if an error occurs.
Throws: As specified in [fs.err.report].
Remarks: The value of member space_info::available is operating system dependent. [ Note: available may be less than free. — end note ]
file_status status(const path& p);
Effects: As if:
error_code ec; file_status result = status(p, ec); if (result.type() == file_type::none) throw filesystem_error(implementation-supplied-message, p, ec); return result;
Returns: See above.
Throws: filesystem_error. [ Note: result values of file_status(file_type::not_found) and file_status(file_type::unknown) are not considered failures and do not cause an exception to be thrown. — end note ]
file_status status(const path& p, error_code& ec) noexcept;
Effects: If possible, determines the attributes of the file p resolves to, as if by using POSIX stat() to obtain a POSIX struct stat. If, during attribute determination, the underlying file system API reports an error, sets ec to indicate the specific error reported. Otherwise, ec.clear(). [ Note: This allows users to inspect the specifics of underlying API errors even when the value returned by status() is not file_status(file_type::none). — end note ]
Let prms denote the result of (m & perms::mask), where m is determined as if by converting the st_mode member of the obtained struct stat to the type perms.
Returns:
If ec != error_code():
If the specific error indicates that p cannot be resolved because some element of the path does not exist, returns file_status(file_type::not_found).
Otherwise, if the specific error indicates that p can be resolved but the attributes cannot be determined, returns file_status(file_type::unknown).
Otherwise, returns file_status(file_type::none).
[ Note: These semantics distinguish between p being known not to exist, p existing but not being able to determine its attributes, and there being an error that prevents even knowing if p exists. These distinctions are important to some use cases. — end note ]
Otherwise,
If the attributes indicate a regular file, as if by POSIX S_ISREG, returns file_status(file_type::regular, prms). [ Note: file_type::regular implies appropriate <fstream> operations would succeed, assuming no hardware, permission, access, or file system race errors. Lack of file_type::regular does not necessarily imply <fstream> operations would fail on a directory. — end note ]
Otherwise, if the attributes indicate a directory, as if by POSIX S_ISDIR, returns file_status(file_type::directory, prms). [ Note: file_type::directory implies directory_iterator(p) would succeed. — end note ]
Otherwise, if the attributes indicate a block special file, as if by POSIX S_ISBLK, returns file_status(file_type::block, prms).
Otherwise, if the attributes indicate a character special file, as if by POSIX S_ISCHR, returns file_status(file_type::character, prms).
Otherwise, if the attributes indicate a fifo or pipe file, as if by POSIX S_ISFIFO, returns file_status(file_type::fifo, prms).
Otherwise, if the attributes indicate a socket, as if by POSIX S_ISSOCK, returns file_status(file_type::socket, prms).
Otherwise, returns file_status(file_type::unknown, prms).
Remarks: If a symbolic link is encountered during pathname resolution, pathname resolution continues using the contents of the symbolic link.
bool status_known(file_status s) noexcept;
Returns: s.type() != file_type::none.
file_status symlink_status(const path& p);
file_status symlink_status(const path& p, error_code& ec) noexcept;
Effects: Same as status(), above, except that the attributes of p are determined as if by using POSIX lstat() to obtain a POSIX struct stat.
Let prms denote the result of (m & perms::mask), where m is determined as if by converting the st_mode member of the obtained struct stat to the type perms.
Returns: Same as status(), above, except that if the attributes indicate a symbolic link, as if by POSIX S_ISLNK, returns file_status(file_type::symlink, prms). The signature with argument ec returns file_status(file_type::none) if an error occurs.
Remarks: Pathname resolution terminates if p names a symbolic link.
Throws: As specified in [fs.err.report].
path system_complete(const path& p);
path system_complete(const path& p, error_code& ec);
Effects: Composes an absolute path from p, using the same rules used by the operating system to resolve a path passed as the filename argument to standard library open functions.
Returns: The composed path. The signature with argument ec returns path() if an error occurs.
Postconditions: For the returned path, rp, rp.is_absolute() is true.
Throws: As specified in [fs.err.report].
[ Example: For POSIX-based operating systems, system_complete(p) has the same semantics as absolute(p, current_path()).
For Windows-based operating systems, system_complete(p) has the same semantics as absolute(p, current_path()) if p.is_absolute() || !p.has_root_name() or p and current_path() have the same root_name(). Otherwise system_complete(p) acts as if absolute(p, cwd) is the current directory for the p.root_name() drive. For programs run by the command processor, however, the current directory for the p.root_name() drive may have been set by a prior program, and this may have unintended consequences. — end example ]
path temp_directory_path();
path temp_directory_path(error_code& ec);
Returns: An unspecifed directory path suitable for temporary files. An error shall be reported if !exists(p) || !is_directory(p), where p is the path to be returned. The signature with argument ec returns path() if an error occurs.
Throws: As specified in [fs.err.report].
[ Example: For POSIX-based operating systems, an implementation might return the path supplied by the first environment variable found in the list TMPDIR, TMP, TEMP, TEMPDIR, or if none of these are found, "/tmp".
For Windows-based operating systems, an implementation might return the path reported by the Windows GetTempPath API function. — end example ]
path weakly_canonical(const path& p);
path weakly_canonical(const path& p, error_code& ec);
Returns: p with symlinks resolved and the result normalized ([fs.def.normal.form]).
Effects: Using status(p) or status(p, ec), respectively, to determine existence, return a path composed by operator/= from the result of calling canonical() without a base argument and with a path argument composed of the leading elements of p that exist, if any, followed by the elements of p that do not exist, if any. For the first form, canonical() is called without an error_code argument. For the second form, canonical() is called with ec as an error_code argument, and path() is returned at the first error occurrence, if any.
Postconditions: The returned path is in normal form ([fs.def.normal.form]).
Remarks: Implementations are encouraged to avoid unnecessary normalization such as when canonical() has already been called on the entirety of p.
Throws: As specified in [fs.err.report].
namespace std {
using size_t = see [support.types.layout];
using FILE = see below;
using fpos_t = see below;
}
#define NULL see [support.types.nullptr]
#define _IOFBF see below
#define _IOLBF see below
#define _IONBF see below
#define BUFSIZ see below
#define EOF see below
#define FOPEN_MAX see below
#define FILENAME_MAX see below
#define L_tmpnam see below
#define SEEK_CUR see below
#define SEEK_END see below
#define SEEK_SET see below
#define TMP_MAX see below
#define stderr see below
#define stdin see below
#define stdout see below
namespace std {
int remove(const char* filename);
int rename(const char* old, const char* new);
FILE* tmpfile();
char* tmpnam(char* s);
int fclose(FILE* stream);
int fflush(FILE* stream);
FILE* fopen(const char* filename, const char* mode);
FILE* freopen(const char* filename, const char* mode, FILE* stream);
void setbuf(FILE* stream, char* buf);
int setvbuf(FILE* stream, char* buf, int mode, size_t size);
int fprintf(FILE* stream, const char* format, ...);
int fscanf(FILE* stream, const char* format, ...);
int printf(const char* format, ...);
int scanf(const char* format, ...);
int snprintf(char* s, size_t n, const char* format, ...);
int sprintf(char* s, const char* format, ...);
int sscanf(const char* s, const char* format, ...);
int vfprintf(FILE* stream, const char* format, va_list arg);
int vfscanf(FILE* stream, const char* format, va_list arg);
int vprintf(const char* format, va_list arg);
int vscanf(const char* format, va_list arg);
int vsnprintf(char* s, size_t n, const char* format, va_list arg);
int vsprintf(char* s, const char* format, va_list arg);
int vsscanf(const char* s, const char* format, va_list arg);
int fgetc(FILE* stream);
char* fgets(char* s, int n, FILE* stream);
int fputc(int c, FILE* stream);
int fputs(const char* s, FILE* stream);
int getc(FILE* stream);
int getchar();
int putc(int c, FILE* stream);
int putchar(int c);
int puts(const char* s);
int ungetc(int c, FILE* stream);
size_t fread(void* ptr, size_t size, size_t nmemb, FILE* stream);
size_t fwrite(const void* ptr, size_t size, size_t nmemb, FILE* stream);
int fgetpos(FILE* stream, fpos_t* pos);
int fseek(FILE* stream, long int offset, int whence);
int fsetpos(FILE* stream, const fpos_t* pos);
long int ftell(FILE* stream);
void rewind(FILE* stream);
void clearerr(FILE* stream);
int feof(FILE* stream);
int ferror(FILE* stream);
void perror(const char* s);
}
The contents and meaning of the header <cstdio> are the same as the C standard library header <stdio.h>.
Calls to the function tmpnam with an argument that is a null pointer value may introduce a data race ([res.on.data.races]) with other calls to tmpnam with an argument that is a null pointer value.
See also: ISO C 7.21.
#include <cstdint>
namespace std {
using imaxdiv_t = see below;
intmax_t imaxabs(intmax_t j);
imaxdiv_t imaxdiv(intmax_t numer, intmax_t denom);
intmax_t strtoimax(const char* nptr, char** endptr, int base);
uintmax_t strtoumax(const char* nptr, char** endptr, int base);
intmax_t wcstoimax(const wchar_t* nptr, wchar_t** endptr, int base);
uintmax_t wcstoumax(const wchar_t* nptr, wchar_t** endptr, int base);
intmax_t abs(intmax_t); // optional, see below
imaxdiv_t div(intmax_t, intmax_t); // optional, see below
}
#define PRIdN see below
#define PRIiN see below
#define PRIoN see below
#define PRIuN see below
#define PRIxN see below
#define PRIXN see below
#define SCNdN see below
#define SCNiN see below
#define SCNoN see below
#define SCNuN see below
#define SCNxN see below
#define PRIdLEASTN see below
#define PRIiLEASTN see below
#define PRIoLEASTN see below
#define PRIuLEASTN see below
#define PRIxLEASTN see below
#define PRIXLEASTN see below
#define SCNdLEASTN see below
#define SCNiLEASTN see below
#define SCNoLEASTN see below
#define SCNuLEASTN see below
#define SCNxLEASTN see below
#define PRIdFASTN see below
#define PRIiFASTN see below
#define PRIoFASTN see below
#define PRIuFASTN see below
#define PRIxFASTN see below
#define PRIXFASTN see below
#define SCNdFASTN see below
#define SCNiFASTN see below
#define SCNoFASTN see below
#define SCNuFASTN see below
#define SCNxFASTN see below
#define PRIdMAX see below
#define PRIiMAX see below
#define PRIoMAX see below
#define PRIuMAX see below
#define PRIxMAX see below
#define PRIXMAX see below
#define SCNdMAX see below
#define SCNiMAX see below
#define SCNoMAX see below
#define SCNuMAX see below
#define SCNxMAX see below
#define PRIdPTR see below
#define PRIiPTR see below
#define PRIoPTR see below
#define PRIuPTR see below
#define PRIxPTR see below
#define PRIXPTR see below
#define SCNdPTR see below
#define SCNiPTR see below
#define SCNoPTR see below
#define SCNuPTR see below
#define SCNxPTR see below
The contents and meaning of header <cinttypes> are the same as the C standard library header <inttypes.h>, with the following changes:
the header <cinttypes> includes the header <cstdint> instead of <stdint.h>, and
if and only if the type intmax_t designates an extended integer type ([basic.fundamental]), the following function signatures are added:
intmax_t abs(intmax_t); imaxdiv_t div(intmax_t, intmax_t);
which shall have the same semantics as the function signatures intmax_t imaxabs(intmax_t) and imaxdiv_t imaxdiv(intmax_t, intmax_t), respectively.
See also: ISO C 7.8.