31 Input/output library [input.output]

31.5 Iostreams base classes [iostreams.base]

31.5.2 Class ios_base [ios.base]

31.5.2.2 Types [ios.types]

31.5.2.2.1 Class ios_base​::​failure [ios.failure]

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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); }; }
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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 1: 
When ios_base​::​failure is a synonym for another type, that type needs to 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.
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When throwing ios_base​::​failure exceptions, implementations should provide values of ec that identify the specific reason for the failure.
[Note 2: 
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]
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explicit failure(const string& msg, const error_code& ec = io_errc::stream);
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Effects: Constructs the base class with msg and ec.
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explicit failure(const char* msg, const error_code& ec = io_errc::stream);
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Effects: Constructs the base class with msg and ec.

31.5.2.2.2 Type ios_base​::​fmtflags [ios.fmtflags]

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using fmtflags = T1;
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The type fmtflags is a bitmask type ([bitmask.types]).
Setting its elements has the effects indicated in Table 136.
Table 136 — fmtflags effects [tab:ios.fmtflags]
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Element
Effect(s) if set
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boolalpha
insert and extract bool type in alphabetic format
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dec
converts integer input or generates integer output in decimal base
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fixed
generate floating-point output in fixed-point notation
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hex
converts integer input or generates integer output in hexadecimal base
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internal
adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated
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left
adds fill characters on the right (final positions) of certain generated output
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oct
converts integer input or generates integer output in octal base
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right
adds fill characters on the left (initial positions) of certain generated output
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scientific
generates floating-point output in scientific notation
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showbase
generates a prefix indicating the numeric base of generated integer output
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showpoint
generates a decimal-point character unconditionally in generated floating-point output
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showpos
generates a + sign in non-negative generated numeric output
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skipws
skips leading whitespace before certain input operations
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unitbuf
flushes output after each output operation
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uppercase
replaces certain lowercase letters with their uppercase equivalents in generated output
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Type fmtflags also defines the constants indicated in Table 137.
Table 137 — fmtflags constants [tab:ios.fmtflags.const]
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Constant
Allowable values
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adjustfield
left | right | internal
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basefield
dec | oct | hex
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floatfield
scientific | fixed

31.5.2.2.3 Type ios_base​::​iostate [ios.iostate]

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using iostate = T2;
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The type iostate is a bitmask type ([bitmask.types]) that contains the elements indicated in Table 138.
Table 138 — iostate effects [tab:ios.iostate]
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Element
Effect(s) if set
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badbit
indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file);
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eofbit
indicates that an input operation reached the end of an input sequence;
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failbit
indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.
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Type iostate also defines the constant:

31.5.2.2.4 Type ios_base​::​openmode [ios.openmode]

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using openmode = T3;
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The type openmode is a bitmask type ([bitmask.types]).
It contains the elements indicated in Table 139.
Table 139 — openmode effects [tab:ios.openmode]
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Element
Effect(s) if set
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app
seek to end before each write
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ate
open and seek to end immediately after opening
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binary
perform input and output in binary mode (as opposed to text mode)
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in
open for input
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noreplace
open in exclusive mode
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out
open for output
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trunc
truncate an existing stream when opening

31.5.2.2.5 Type ios_base​::​seekdir [ios.seekdir]

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using seekdir = T4;
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The type seekdir is an enumerated type ([enumerated.types]) that contains the elements indicated in Table 140.
Table 140 — seekdir effects [tab:ios.seekdir]
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Element
Meaning
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beg
request a seek (for subsequent input or output) relative to the beginning of the stream
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cur
request a seek relative to the current position within the sequence
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end
request a seek relative to the current end of the sequence

31.5.2.2.6 Class ios_base​::​Init [ios.init]

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namespace std { class ios_base::Init { public: Init(); Init(const Init&) = default; ~Init(); Init& operator=(const Init&) = default; }; }
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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>.
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Init();
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Effects: Constructs and initializes the objects cin, cout, cerr, clog, wcin, wcout, wcerr, and wclog if they have not already been constructed and initialized.
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~Init();
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Effects: If there are no other instances of the class still in existence, calls cout.flush(), cerr.flush(), clog.flush(), wcout.flush(), wcerr.flush(), wclog.flush().