29 Input/output library [input.output]

29.7 Formatting and manipulators [iostream.format]

29.7.1 Header <istream> synopsis [istream.syn]

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);
}

29.7.2 Header <ostream> synopsis [ostream.syn]

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>
    basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os);
  template<class charT, class traits>
    basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os);
  template<class charT, class traits>
    basic_ostream<charT, traits>& flush_emit(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);
}

29.7.3 Header <iomanip> synopsis [iomanip.syn]

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<class 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('\\'));

  template<class charT, class traits>
    T14 quoted(basic_string_view<charT, traits> s,
               charT delim = charT('"'), charT escape = charT('\\'));
}

29.7.4 Input streams [input.streams]

1
#
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.

29.7.4.1 Class template basic_­istream [istream]

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)
    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&) = delete;
    basic_istream(basic_istream&& rhs);

    // [istream.assign], assign and swap
    basic_istream& operator=(const basic_istream&) = 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, size_t N>
    basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>&, charT(&)[N]);
  template<class traits, size_t N>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, unsigned char(&)[N]);
  template<class traits, size_t N>
    basic_istream<char, traits>& operator>>(basic_istream<char, traits>&, signed char(&)[N]);
}
1
#
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.
2
#
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.
3
#
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.
4
#
If one of these called functions throws an exception, then unless explicitly noted otherwise, the input function sets badbit in the error state.
If badbit is set 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.

29.7.4.1.1 Constructors [istream.cons]

🔗
explicit basic_istream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobject with basic_­ios​::​init(sb) ([basic.ios.cons]).
2
#
Postconditions: gcount() == 0.
🔗
basic_istream(basic_istream&& rhs);
3
#
Effects: Default constructs the base class, copies the gcount() from rhs, calls basic_­ios<charT, traits>​::​move(rhs) to initialize the base class, and sets the gcount() for rhs to 0.
🔗
virtual ~basic_istream();
4
#
Remarks: Does not perform any operations of rdbuf().

29.7.4.1.2 Assignment and swap [istream.assign]

🔗
basic_istream& operator=(basic_istream&& rhs);
1
#
Effects: Equivalent to: swap(rhs).
2
#
Returns: *this.
🔗
void swap(basic_istream& rhs);
3
#
Effects: Calls basic_­ios<charT, traits>​::​swap(rhs).
Exchanges the values returned by gcount() and rhs.gcount().

29.7.4.1.3 Class basic_­istream​::​sentry [istream.sentry]

namespace std {
  template<class charT, class traits = char_traits<charT>>
  class basic_istream<charT, traits>::sentry {
    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;
  };
}
1
#
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);
2
#
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.301
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).
3
#
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.
4
#
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.
5
#
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])).302
🔗
~sentry();
6
#
Effects: None.
🔗
explicit operator bool() const;
7
#
Returns: ok_­.
301)
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.
⮥
302)
The sentry constructor and destructor can also perform additional implementation-dependent operations.
⮥

29.7.4.2 Formatted input functions [istream.formatted]

29.7.4.2.1 Common requirements [istream.formatted.reqmts]

1
#
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_­base​::​badbit is turned on303 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.
303)
This is done without causing an ios_­base​::​failure to be thrown.
⮥

29.7.4.2.2 Arithmetic extractors [istream.formatted.arithmetic]

🔗
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);
1
#
As in the case of the inserters, these extractors depend on the locale's 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.
🔗
operator>>(short& val);
2
#
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);
🔗
operator>>(int& val);
3
#
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);

29.7.4.2.3 basic_­istream​::​operator>> [istream.extractors]

🔗
basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&));
1
#
Effects: None.
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
2
#
Returns: pf(*this).304
🔗
basic_istream<charT, traits>& operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
3
#
Effects: Calls pf(*this).
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
4
#
Returns: *this.
🔗
basic_istream<charT, traits>& operator>>(ios_base& (*pf)(ios_base&));
5
#
Effects: Calls pf(*this).305
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
6
#
Returns: *this.
🔗
template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in, charT (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, unsigned char (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, signed char (&s)[N]);
7
#
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 s.
If width() is greater than zero, n is min(size_­t(width()), N).
Otherwise n is N.
n is the maximum number of characters stored.
8
#
Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n-1 characters are stored;
  • (8.2)
    end of file occurs on the input sequence;
  • (8.3)
    letting ct be use_­facet<ctype<charT>>(in.getloc()), ct.is(ct.space, c) is true.
9
#
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).
10
#
If the function extracted no characters, it calls setstate(failbit), which may throw ios_­base​::​​failure ([iostate.flags]).
11
#
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);
12
#
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).
13
#
Returns: in.
🔗
basic_istream<charT, traits>& operator>>(basic_streambuf<charT, traits>* sb);
14
#
Effects: Behaves as an unformatted input function.
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:
  • (14.1)
    end-of-file occurs on the input sequence;
  • (14.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (14.3)
    an exception occurs (in which case the exception is caught).
15
#
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 set in exceptions() ([iostate.flags]), then the caught exception is rethrown.
16
#
Returns: *this.
304)
See, for example, the function signature ws(basic_­istream&) ([istream.manip]).
⮥
305)
See, for example, the function signature dec(ios_­base&).
⮥

29.7.4.3 Unformatted input functions [istream.unformatted]

1
#
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_­base​::​badbit is turned on306 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.
🔗
streamsize gcount() const;
2
#
Effects: None.
This member function does not behave as an unformatted input function (as described above).
3
#
Returns: The number of characters extracted by the last unformatted input member function called for the object.
🔗
int_type get();
4
#
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]).
5
#
Returns: c if available, otherwise traits​::​eof().
🔗
basic_istream<charT, traits>& get(char_type& c);
6
#
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.307
Otherwise, the function calls setstate(failbit) (which may throw ios_­base​::​failure ([iostate.flags])).
7
#
Returns: *this.
🔗
basic_istream<charT, traits>& get(char_type* s, streamsize n, char_type delim);
8
#
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.308
Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n is less than one or n - 1 characters are stored;
  • (8.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));
  • (8.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted).
9
#
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.
10
#
Returns: *this.
🔗
basic_istream<charT, traits>& get(char_type* s, streamsize n);
11
#
Effects: Calls get(s, n, widen('\n')).
12
#
Returns: Value returned by the call.
🔗
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb, char_type delim);
13
#
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:
  • (13.1)
    end-of-file occurs on the input sequence;
  • (13.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (13.3)
    traits​::​eq(c, delim) for the next available input character c (in which case c is not extracted);
  • (13.4)
    an exception occurs (in which case, the exception is caught but not rethrown).
14
#
If the function inserts no characters, it calls setstate(failbit), which may throw ios_­base​::​​failure ([iostate.flags]).
15
#
Returns: *this.
🔗
basic_istream<charT, traits>& get(basic_streambuf<char_type, traits>& sb);
16
#
Effects: Calls get(sb, widen('\n')).
17
#
Returns: Value returned by the call.
🔗
basic_istream<charT, traits>& getline(char_type* s, streamsize n, char_type delim);
18
#
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.309
Characters are extracted and stored until one of the following occurs:
  1. 1.end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit));
  2. 2.traits​::​eq(c, delim) for the next available input character c (in which case the input character is extracted but not stored);310
  3. 3.n is less than one or n - 1 characters are stored (in which case the function calls setstate(​failbit)).
19
#
These conditions are tested in the order shown.311
20
#
If the function extracts no characters, it calls setstate(failbit) (which may throw ios_­base​::​​failure ([iostate.flags])).312
21
#
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.
22
#
Returns: *this.
23
#
[ 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);
24
#
Returns: getline(s, n, widen('\n'))
🔗
basic_istream<charT, traits>& ignore(streamsize n = 1, int_type delim = traits::eof());
25
#
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:
  • (25.1)
    n != numeric_­limits<streamsize>​::​max() and n characters have been extracted so far
  • (25.2)
    end-of-file occurs on the input sequence (in which case the function calls setstate(eofbit), which may throw ios_­base​::​failure ([iostate.flags]));
  • (25.3)
    traits​::​eq_­int_­type(traits​::​to_­int_­type(c), delim) for the next available input character c (in which case c is extracted).
26
#
Remarks: The last condition will never occur if traits​::​eq_­int_­type(delim, traits​::​eof()).
27
#
Returns: *this.
🔗
int_type peek();
28
#
Effects: Behaves as an unformatted input function (as described above).
After constructing a sentry object, reads but does not extract the current input character.
29
#
Returns: traits​::​eof() if good() is false.
Otherwise, returns rdbuf()->sgetc().
🔗
basic_istream<charT, traits>& read(char_type* s, streamsize n);
30
#
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.313
Characters are extracted and stored until either of the following occurs:
  • (30.1)
    n characters are stored;
  • (30.2)
    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])).
31
#
Returns: *this.
🔗
streamsize readsome(char_type* s, streamsize n);
32
#
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;
  • (32.1)
    If rdbuf()->in_­avail() == 0, extracts no characters
  • (32.2)
    If rdbuf()->in_­avail() > 0, extracts min(rdbuf()->in_­avail(), n)).
33
#
Returns: The number of characters extracted.
🔗
basic_istream<charT, traits>& putback(char_type c);
34
#
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(c).
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
 ]
35
#
Returns: *this.
🔗
basic_istream<charT, traits>& unget();
36
#
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
 ]
37
#
Returns: *this.
🔗
int sync();
38
#
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.
🔗
pos_type tellg();
39
#
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().
40
#
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);
41
#
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).
42
#
Returns: *this.
🔗
basic_istream<charT, traits>& seekg(off_type off, ios_base::seekdir dir);
43
#
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).
44
#
Returns: *this.
306)
This is done without causing an ios_­base​::​failure to be thrown.
⮥
307)
Note that this function is not overloaded on types signed char and unsigned char.
⮥
308)
Note that this function is not overloaded on types signed char and unsigned char.
⮥
309)
Note that this function is not overloaded on types signed char and unsigned char.
⮥
310)
Since the final input character is “extracted”, it is counted in the gcount(), even though it is not stored.
⮥
311)
This allows an input line which exactly fills the buffer, without setting failbit.
This is different behavior than the historical AT&T implementation.
⮥
312)
This implies an empty input line will not cause failbit to be set.
⮥
313)
Note that this function is not overloaded on types signed char and unsigned char.
⮥

29.7.4.4 Standard basic_­istream manipulators [istream.manip]

1
#
Each instantiation of the function template specified in this subclause is a designated addressable function ([namespace.std]).
🔗
template<class charT, class traits> basic_istream<charT, traits>& ws(basic_istream<charT, traits>& is);
2
#
Effects: Behaves as an unformatted input function, 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.
If ws stops extracting characters because there are no more available it sets eofbit, but not failbit.
3
#
Returns: is.

29.7.4.5 Rvalue stream extraction [istream.rvalue]

🔗
template<class Istream, class T> Istream&& operator>>(Istream&& is, T&& x);
1
#
Constraints: The expression is >> std​::​forward<T>(x) is well-formed when treated as an unevaluated operand and Istream is publicly and unambiguously derived from ios_­base.
2
#
Effects: Equivalent to: 
is >> std::forward<T>(x);
return std::move(is);

29.7.4.6 Class template basic_­iostream [iostreamclass]

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&) = delete;
    basic_iostream(basic_iostream&& rhs);

    // [iostream.assign], assign and swap
    basic_iostream& operator=(const basic_iostream&) = delete;
    basic_iostream& operator=(basic_iostream&& rhs);
    void swap(basic_iostream& rhs);
  };
}
1
#
The class template basic_­iostream inherits a number of functions that allow reading input and writing output to sequences controlled by a stream buffer.

29.7.4.6.1 Constructors [iostream.cons]

🔗
explicit basic_iostream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobjects with basic_­istream<charT, traits>(sb) ([istream]) and basic_­ostream<charT, traits>(sb).
2
#
Postconditions: rdbuf() == sb and gcount() == 0.
🔗
basic_iostream(basic_iostream&& rhs);
3
#
Effects: Move constructs from the rvalue rhs by constructing the basic_­istream base class with move(rhs).

29.7.4.6.2 Destructor [iostream.dest]

🔗
virtual ~basic_iostream();
1
#
Remarks: Does not perform any operations on rdbuf().

29.7.4.6.3 Assignment and swap [iostream.assign]

🔗
basic_iostream& operator=(basic_iostream&& rhs);
1
#
Effects: Equivalent to: swap(rhs).
🔗
void swap(basic_iostream& rhs);
2
#
Effects: Calls basic_­istream<charT, traits>​::​swap(rhs).

29.7.5 Output streams [output.streams]

1
#
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.

29.7.5.1 Class template basic_­ostream [ostream]

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)
    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&) = delete;
    basic_ostream(basic_ostream&& rhs);

    // [ostream.assign], assign and swap
    basic_ostream& operator=(const basic_ostream&) = 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 traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, wchar_t) = delete;
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char8_t) = delete;
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char16_t) = delete;
  template<class traits>
    basic_ostream<char, traits>& operator<<(basic_ostream<char, traits>&, char32_t) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, char8_t) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, char16_t) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, char32_t) = delete;

  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*);

  template<class traits>
    basic_ostream<char, traits>&
      operator<<(basic_ostream<char, traits>&, const wchar_t*) = delete;
  template<class traits>
    basic_ostream<char, traits>&
      operator<<(basic_ostream<char, traits>&, const char8_t*) = delete;
  template<class traits>
    basic_ostream<char, traits>&
      operator<<(basic_ostream<char, traits>&, const char16_t*) = delete;
  template<class traits>
    basic_ostream<char, traits>&
      operator<<(basic_ostream<char, traits>&, const char32_t*) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, const char8_t*) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, const char16_t*) = delete;
  template<class traits>
    basic_ostream<wchar_t, traits>&
      operator<<(basic_ostream<wchar_t, traits>&, const char32_t*) = delete;
}
1
#
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.
2
#
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().
3
#
If one of these called functions throws an exception, then unless explicitly noted otherwise the output function sets badbit in the error state.
If badbit is set in exceptions(), the output 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.
4
#
[ Note
:
The deleted overloads of operator<< prevent formatting characters as integers and strings as pointers.
— end note
 ]

29.7.5.1.1 Constructors [ostream.cons]

🔗
explicit basic_ostream(basic_streambuf<charT, traits>* sb);
1
#
Effects: Initializes the base class subobject with basic_­ios<charT, traits>​::​init(sb) ([basic.ios.cons]).
2
#
Postconditions: rdbuf() == sb.
🔗
basic_ostream(basic_ostream&& rhs);
3
#
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.
🔗
virtual ~basic_ostream();
4
#
Remarks: Does not perform any operations on rdbuf().

29.7.5.1.2 Assignment and swap [ostream.assign]

🔗
basic_ostream& operator=(basic_ostream&& rhs);
1
#
Effects: Equivalent to: swap(rhs).
2
#
Returns: *this.
🔗
void swap(basic_ostream& rhs);
3
#
Effects: Calls basic_­ios<charT, traits>​::​swap(rhs).

29.7.5.1.3 Class basic_­ostream​::​sentry [ostream.sentry]

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;
  };
}
1
#
The class sentry defines a class that is responsible for doing exception safe prefix and suffix operations.
🔗
explicit sentry(basic_ostream<charT, traits>& os);
2
#
If os.good() is nonzero, prepares for formatted or unformatted output.
If os.tie() is not a null pointer, calls os.tie()->flush().314
3
#
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])).315
🔗
~sentry();
4
#
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;
5
#
Effects: Returns ok_­.
314)
The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.
⮥
315)
The sentry constructor and destructor can also perform additional implementation-dependent operations.
⮥

29.7.5.1.4 Seek members [ostream.seeks]

1
#
Each seek member function begins execution by constructing an object of class sentry.
It returns by destroying the sentry object.
🔗
pos_type tellp();
2
#
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);
3
#
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).
4
#
Returns: *this.
🔗
basic_ostream<charT, traits>& seekp(off_type off, ios_base::seekdir dir);
5
#
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).
6
#
Returns: *this.

29.7.5.2 Formatted output functions [ostream.formatted]

29.7.5.2.1 Common requirements [ostream.formatted.reqmts]

1
#
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_­base​::​badbit is turned on316 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.
2
#
The descriptions of the individual formatted output functions describe how they perform output and do not mention the sentry object.
3
#
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.
316)
without causing an ios_­base​::​failure to be thrown.
⮥

29.7.5.2.2 Arithmetic inserters [ostream.inserters.arithmetic]

🔗
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);
1
#
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();
2
#
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 class 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.
3
#
Returns: *this.

29.7.5.2.3 basic_­ostream​::​operator<< [ostream.inserters]

🔗
basic_ostream<charT, traits>& operator<<(basic_ostream<charT, traits>& (*pf)(basic_ostream<charT, traits>&));
1
#
Effects: None.
Does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
2
#
Returns: pf(*this).317
🔗
basic_ostream<charT, traits>& operator<<(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
3
#
Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
4
#
Returns: *this.318
🔗
basic_ostream<charT, traits>& operator<<(ios_base& (*pf)(ios_base&));
5
#
Effects: Calls pf(*this).
This inserter does not behave as a formatted output function (as described in [ostream.formatted.reqmts]).
6
#
Returns: *this.
🔗
basic_ostream<charT, traits>& operator<<(basic_streambuf<charT, traits>* sb);
7
#
Effects: Behaves as an unformatted output function.
After the sentry object is constructed, if sb is null calls setstate(badbit) (which may throw ios_­base​::​failure).
8
#
Gets characters from sb and inserts them in *this.
Characters are read from sb and inserted until any of the following occurs:
  • (8.1)
    end-of-file occurs on the input sequence;
  • (8.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (8.3)
    an exception occurs while getting a character from sb.
9
#
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 the error state, and if failbit is set in exceptions() the caught exception is rethrown.
10
#
Returns: *this.
🔗
basic_ostream<charT, traits>& operator<<(nullptr_t);
11
#
Effects: Equivalent to: 
return *this << s;
where s is an implementation-defined NTCTS.
317)
See, for example, the function signature endl(basic_­ostream&) ([ostream.manip]).
⮥
318)
See, for example, the function signature dec(ios_­base&) ([basefield.manip]).
⮥

29.7.5.2.4 Character inserter function templates [ostream.inserters.character]

🔗
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);
1
#
Effects: Behaves as a formatted output function 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).
2
#
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);
3
#
Preconditions: s is not a null pointer.
4
#
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:
  • (4.1)
    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*,
  • (4.2)
    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*,
  • (4.3)
    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).
5
#
Returns: out.

29.7.5.3 Unformatted output functions [ostream.unformatted]

1
#
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_­base​::​badbit is turned on319 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.
🔗
basic_ostream<charT, traits>& put(char_type c);
2
#
Effects: Behaves as an unformatted output function (as described above).
After constructing a sentry object, inserts the character c, if possible.320
3
#
Otherwise, calls setstate(badbit) (which may throw ios_­base​::​failure ([iostate.flags])).
4
#
Returns: *this.
🔗
basic_ostream& write(const char_type* s, streamsize n);
5
#
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.321
Characters are inserted until either of the following occurs:
  • (5.1)
    n characters are inserted;
  • (5.2)
    inserting in the output sequence fails (in which case the function calls setstate(badbit), which may throw ios_­base​::​failure ([iostate.flags])).
6
#
Returns: *this.
🔗
basic_ostream& flush();
7
#
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.
8
#
Returns: *this.
319)
without causing an ios_­base​::​failure to be thrown.
⮥
320)
Note that this function is not overloaded on types signed char and unsigned char.
⮥
321)
Note that this function is not overloaded on types signed char and unsigned char.
⮥

29.7.5.4 Standard manipulators [ostream.manip]

1
#
Each instantiation of any of the function templates specified in this subclause is a designated addressable function ([namespace.std]).
🔗
template<class charT, class traits> basic_ostream<charT, traits>& endl(basic_ostream<charT, traits>& os);
2
#
Effects: Calls os.put(os.widen('\n')), then os.flush().
3
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& ends(basic_ostream<charT, traits>& os);
4
#
Effects: Inserts a null character into the output sequence: calls os.put(charT()).
5
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& flush(basic_ostream<charT, traits>& os);
6
#
Effects: Calls os.flush().
7
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& emit_on_flush(basic_ostream<charT, traits>& os);
8
#
Effects: If os.rdbuf() is a basic_­syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_­emit_­on_­sync(true).
Otherwise this manipulator has no effect.
[ Note
:
To work around the issue that the Allocator template argument cannot be deduced, implementations can introduce an intermediate base class to basic_­syncbuf that manages its emit_­on_­sync flag.
— end note
 ]
9
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& noemit_on_flush(basic_ostream<charT, traits>& os);
10
#
Effects: If os.rdbuf() is a basic_­syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->set_­emit_­on_­sync(false).
Otherwise this manipulator has no effect.
11
#
Returns: os.
🔗
template<class charT, class traits> basic_ostream<charT, traits>& flush_emit(basic_ostream<charT, traits>& os);
12
#
Effects: Calls os.flush().
Then, if os.rdbuf() is a basic_­syncbuf<charT, traits, Allocator>*, called buf for the purpose of exposition, calls buf->emit().
13
#
Returns: os.

29.7.5.5 Rvalue stream insertion [ostream.rvalue]

🔗
template<class Ostream, class T> Ostream&& operator<<(Ostream&& os, const T& x);
1
#
Constraints: The expression os << x is well-formed when treated as an unevaluated operand and Ostream is publicly and unambiguously derived from ios_­base.
2
#
Effects: As if by: os << x;
3
#
Returns: std​::​move(os).

29.7.6 Standard manipulators [std.manip]

1
#
The header <iomanip> defines several functions that support extractors and inserters that alter information maintained by class ios_­base and its derived classes.
🔗
unspecified resetiosflags(ios_base::fmtflags mask);
2
#
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:322
void f(ios_base& str, ios_base::fmtflags mask) {
  // reset specified flags
  str.setf(ios_base::fmtflags(0), mask);
}
The expression out << resetiosflags(mask) has type basic_­ostream<charT, traits>& and value out.
The expression in >> resetiosflags(mask) has type basic_­istream<charT, traits>& and value in.
🔗
unspecified setiosflags(ios_base::fmtflags mask);
3
#
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) has type basic_­ostream<charT, traits>& and value out.
The expression in >> setiosflags(mask) has type basic_­istream<charT, traits>& and value in.
🔗
unspecified setbase(int base);
4
#
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) has type basic_­ostream<charT, traits>& and value out.
The expression in >> setbase(base) has type basic_­istream<charT, traits>& and value in.
🔗
unspecified setfill(char_type c);
5
#
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) has type basic_­ostream<charT, traits>& and value out.
🔗
unspecified setprecision(int n);
6
#
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) has type basic_­ostream<charT, traits>& and value out.
The expression in >> setprecision(n) has type basic_­istream<charT, traits>& and value in.
🔗
unspecified setw(int n);
7
#
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) has type basic_­ostream<charT, traits>& and value out.
The expression in >> setw(n) has type basic_­istream<charT, traits>& and value in.
322)
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).
⮥

29.7.7 Extended manipulators [ext.manip]

1
#
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);
2
#
Mandates: The type moneyT is either long double or a specialization of the basic_­string template ([strings]).
3
#
Effects: The expression in >> get_­money(mon, intl) described below behaves as a formatted input function.
4
#
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) has type basic_­istream<charT, traits>& and value in.
🔗
template<class moneyT> unspecified put_money(const moneyT& mon, bool intl = false);
5
#
Mandates: The type moneyT is either long double or a specialization of the basic_­string template ([strings]).
6
#
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 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_base::badbit);
}
The expression out << put_­money(mon, intl) has type basic_­ostream<charT, traits>& and value out.
🔗
template<class charT> unspecified get_time(struct tm* tmb, const charT* fmt);
7
#
Preconditions: The argument tmb is a valid pointer to an object of type struct tm, and [fmt, fmt + char_­traits<charT>​::​length(fmt)) is a valid range.
8
#
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) has type basic_­istream<charT, traits>& and value in.
🔗
template<class charT> unspecified put_time(const struct tm* tmb, const charT* fmt);
9
#
Preconditions: The argument tmb is a valid pointer to an object of type struct tm, and [fmt, fmt + char_­traits<charT>​::​length(fmt)) is a valid range.
10
#
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) has type basic_­ostream<charT, traits>& and value out.

29.7.8 Quoted manipulators [quoted.manip]

1
#
[ 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('\\')); template<class charT, class traits> unspecified quoted(basic_string_view<charT, traits> s, charT delim = charT('"'), charT escape = charT('\\'));
2
#
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 and third forms is the same as traits, then the expression out << quoted(s, delim, escape) behaves as a formatted output function of out.
This forms a character sequence seq, initially consisting of the following elements:
  • (2.1)
    delim.
  • (2.2)
    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.
  • (2.3)
    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) has 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('\\'));
3
#
Returns: An object of unspecified type such that:
  • (3.1)
    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]):
    • (3.1.1)
      If the first character extracted is equal to delim, as determined by traits_­type​::​eq, then:
      • (3.1.1.1)
        Turn off the skipws flag.
      • (3.1.1.2)
        s.clear()
      • (3.1.1.3)
        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.
      • (3.1.1.4)
        Discard the final delim character.
      • (3.1.1.5)
        Restore the skipws flag to its original value.
    • (3.1.2)
      Otherwise, in >> s.
  • (3.2)
    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.
  • (3.3)
    The expression in >> quoted(s, delim, escape) has type basic_­istream<charT, traits>& and value in.
  • (3.4)
    The expression out << quoted(s, delim, escape) has type basic_­ostream​<charT, traits>& and value out.