std::basic_istream_sentry - Man Page

typedef ctype< _CharT > __ctype_type
typedef __istream_type::__ctype_type __ctype_type
typedef _Traits::int_type __int_type
typedef basic_ios< _CharT, _Traits > __ios_type
typedef basic_istream< _CharT, _Traits > __istream_type
typedef basic_istream< _CharT, _Traits > __istream_type
typedef num_get< _CharT, istreambuf_iterator< _CharT, _Traits > > __num_get_type
typedef basic_streambuf< _CharT, _Traits > __streambuf_type
typedef basic_streambuf< _CharT, _Traits > __streambuf_type
typedef _CharT char_type
enum event
The set of events that may be passed to an event callback.
typedef void(* event_callback) (event __e, ios_base &__b, int __i)
The type of an event callback function.
typedef _Traits::int_type int_type
typedef _Ios_Iostate iostate
This is a bitmask type.
typedef _Traits::off_type off_type
typedef _Ios_Openmode openmode
This is a bitmask type.
typedef _Traits::pos_type pos_type
typedef _Ios_Seekdir seekdir
This is an enumerated type.
typedef _Traits traits_type
typedef _Traits traits_type
Easy access to dependent types.

typedef num_put< _CharT, ostreambuf_iterator< _CharT, _Traits > > __num_put_type

sentry (basic_istream< _CharT, _Traits > &__is, bool __noskipws=false)
The constructor performs all the work.
virtual ~basic_istream ()
Base destructor.
basic_istream< _CharT, _Traits > & _M_extract (_ValueT &__v)
basic_istream< _CharT, _Traits > & _M_extract (_ValueT &__v)
const locale & _M_getloc () const
Locale access.
void _M_setstate (iostate __state)
bool bad () const
Fast error checking.
basic_istream (__streambuf_type *__sb)
Base constructor.
void clear (iostate __state=goodbit)
[Re]sets the error state.
basic_ios & copyfmt (const basic_ios &__rhs)
Copies fields of __rhs into this.
bool eof () const
Fast error checking.
iostate exceptions () const
Throwing exceptions on errors.
void exceptions (iostate __except)
Throwing exceptions on errors.
bool fail () const
Fast error checking.
char_type fill () const
Retrieves the empty character.
char_type fill (char_type __ch)
Sets a new empty character.
fmtflags flags () const
Access to format flags.
fmtflags flags (fmtflags __fmtfl)
Setting new format flags all at once.
streamsize gcount () const
Character counting.
basic_istream< char > & getline (char_type *__s, streamsize __n, char_type __delim)
Explicit specialization declarations, defined in src/istream.cc.
basic_istream< char > & getline (char_type *__s, streamsize __n, char_type __delim)
Explicit specialization declarations, defined in src/istream.cc.
basic_istream< wchar_t > & getline (char_type *__s, streamsize __n, char_type __delim)
basic_istream< wchar_t > & getline (char_type *__s, streamsize __n, char_type __delim)
locale getloc () const
Locale access.
bool good () const
Fast error checking.
basic_istream< char > & ignore (streamsize __n)
basic_istream< char > & ignore (streamsize __n)
basic_istream< wchar_t > & ignore (streamsize __n)
basic_istream< wchar_t > & ignore (streamsize __n)
basic_istream< char > & ignore (streamsize __n, int_type __delim)
basic_istream< char > & ignore (streamsize __n, int_type __delim)
basic_istream< wchar_t > & ignore (streamsize __n, int_type __delim)
basic_istream< wchar_t > & ignore (streamsize __n, int_type __delim)
locale imbue (const locale &__loc)
Moves to a new locale.
long & iword (int __ix)
Access to integer array.
char narrow (char_type __c, char __dfault) const
Squeezes characters.
operator bool () const
Quick status checking.
__istream_type & operator>> (__streambuf_type *__sb)
Extracting into another streambuf.
__istream_type & operator>> (void *&__p)
Basic arithmetic extractors.
streamsize precision () const
Flags access.
streamsize precision (streamsize __prec)
Changing flags.
void *& pword (int __ix)
Access to void pointer array.
basic_streambuf< _CharT, _Traits > * rdbuf () const
Accessing the underlying buffer.
basic_streambuf< _CharT, _Traits > * rdbuf (basic_streambuf< _CharT, _Traits > *__sb)
Changing the underlying buffer.
iostate rdstate () const
Returns the error state of the stream buffer.
void register_callback (event_callback __fn, int __index)
Add the callback __fn with parameter __index.
fmtflags setf (fmtflags __fmtfl)
Setting new format flags.
fmtflags setf (fmtflags __fmtfl, fmtflags __mask)
Setting new format flags.
void setstate (iostate __state)
Sets additional flags in the error state.
basic_ostream< _CharT, _Traits > * tie () const
Fetches the current tied stream.
basic_ostream< _CharT, _Traits > * tie (basic_ostream< _CharT, _Traits > *__tiestr)
Ties this stream to an output stream.
void unsetf (fmtflags __mask)
Clearing format flags.
char_type widen (char __c) const
Widens characters.
streamsize width () const
Flags access.
streamsize width (streamsize __wide)
Changing flags.

__istream_type & operator>> (__istream_type &(*__pf)(__istream_type &))
Interface for manipulators.
__istream_type & operator>> (__ios_type &(*__pf)(__ios_type &))
Interface for manipulators.
__istream_type & operator>> (ios_base &(*__pf)(ios_base &))
Interface for manipulators.

Extractors
All the operator>> functions (aka formatted input functions) have some common behavior. Each starts by constructing a temporary object of type std::basic_istream::sentry with the second argument (noskipws) set to false. This has several effects, concluding with the setting of a status flag; see the sentry documentation for more.

If the sentry status is good, the function tries to extract whatever data is appropriate for the type of the argument.

If an exception is thrown during extraction, ios_base::badbit will be turned on in the stream's error state (without causing an ios_base::failure to be thrown) and the original exception will be rethrown if badbit is set in the exceptions mask.

__istream_type & operator>> (bool &__n)
Integer arithmetic extractors.
__istream_type & operator>> (short &__n)
Integer arithmetic extractors.
__istream_type & operator>> (unsigned short &__n)
Integer arithmetic extractors.
__istream_type & operator>> (int &__n)
Integer arithmetic extractors.
__istream_type & operator>> (unsigned int &__n)
Integer arithmetic extractors.
__istream_type & operator>> (long &__n)
Integer arithmetic extractors.
__istream_type & operator>> (unsigned long &__n)
Integer arithmetic extractors.
__istream_type & operator>> (long long &__n)
Integer arithmetic extractors.
__istream_type & operator>> (unsigned long long &__n)
Integer arithmetic extractors.

__istream_type & operator>> (float &__f)
Floating point arithmetic extractors.
__istream_type & operator>> (double &__f)
Floating point arithmetic extractors.
__istream_type & operator>> (long double &__f)
Floating point arithmetic extractors.

Unformatted Input Functions
All the unformatted input functions have some common behavior. Each starts by constructing a temporary object of type std::basic_istream::sentry with the second argument (noskipws) set to true. This has several effects, concluding with the setting of a status flag; see the sentry documentation for more.

If the sentry status is good, the function tries to extract whatever data is appropriate for the type of the argument.

The number of characters extracted is stored for later retrieval by gcount().

If an exception is thrown during extraction, ios_base::badbit will be turned on in the stream's error state (without causing an ios_base::failure to be thrown) and the original exception will be rethrown if badbit is set in the exceptions mask.

int_type get ()
Simple extraction.
__istream_type & get (char_type &__c)
Simple extraction.
__istream_type & get (char_type *__s, streamsize __n, char_type __delim)
Simple multiple-character extraction.
__istream_type & get (char_type *__s, streamsize __n)
Simple multiple-character extraction.
__istream_type & get (__streambuf_type &__sb, char_type __delim)
Extraction into another streambuf.
__istream_type & get (__streambuf_type &__sb)
Extraction into another streambuf.
__istream_type & getline (char_type *__s, streamsize __n, char_type __delim)
String extraction.
__istream_type & getline (char_type *__s, streamsize __n)
String extraction.
__istream_type & ignore (streamsize __n, int_type __delim)
Discarding characters.
__istream_type & ignore (streamsize __n)
Simple extraction.
__istream_type & ignore ()
Simple extraction.
int_type peek ()
Looking ahead in the stream.
__istream_type & read (char_type *__s, streamsize __n)
Extraction without delimiters.
streamsize readsome (char_type *__s, streamsize __n)
Extraction until the buffer is exhausted, but no more.
__istream_type & putback (char_type __c)
Unextracting a single character.
__istream_type & unget ()
Unextracting the previous character.
int sync ()
Synchronizing the stream buffer.
pos_type tellg ()
Getting the current read position.
__istream_type & seekg (pos_type)
Changing the current read position.
__istream_type & seekg (off_type, ios_base::seekdir)
Changing the current read position.

operator bool () const
The quick-and-easy status check.
bool operator! () const
The quick-and-easy status check.

static bool sync_with_stdio (bool __sync=true)
Interaction with the standard C I/O objects.
static int xalloc ()  throw ()
Access to unique indices.

class __attribute((__abi_tag__('cxx11'))) failure typedef _Ios_Fmtflags fmtflags
These are thrown to indicate problems with io.

static const openmode __noreplace
static const fmtflags adjustfield
A mask of left|right|internal. Useful for the 2-arg form of setf.
static const openmode app
Seek to end before each write.
static const openmode ate
Open and seek to end immediately after opening.
static const iostate badbit
Indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file).
static const fmtflags basefield
A mask of dec|oct|hex. Useful for the 2-arg form of setf.
static const seekdir beg
Request a seek relative to the beginning of the stream.
static const openmode binary
Perform input and output in binary mode (as opposed to text mode). This is probably not what you think it is; see https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary.
static const fmtflags boolalpha
Insert/extract bool in alphabetic rather than numeric format.
static const seekdir cur
Request a seek relative to the current position within the sequence.
static const fmtflags dec
Converts integer input or generates integer output in decimal base.
static const seekdir end
Request a seek relative to the current end of the sequence.
static const iostate eofbit
Indicates that an input operation reached the end of an input sequence.
static const iostate failbit
Indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.
static const fmtflags fixed
Generate floating-point output in fixed-point notation.
static const fmtflags floatfield
A mask of scientific|fixed. Useful for the 2-arg form of setf.
static const iostate goodbit
Indicates all is well.
static const fmtflags hex
Converts integer input or generates integer output in hexadecimal base.
static const openmode in
Open for input. Default for ifstream and fstream.
static const fmtflags internal
Adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated.
static const fmtflags left
Adds fill characters on the right (final positions) of certain generated output. (I.e., the thing you print is flush left.)
static const fmtflags oct
Converts integer input or generates integer output in octal base.
static const openmode out
Open for output. Default for ofstream and fstream.
static const fmtflags right
Adds fill characters on the left (initial positions) of certain generated output. (I.e., the thing you print is flush right.)
static const fmtflags scientific
Generates floating-point output in scientific notation.
static const fmtflags showbase
Generates a prefix indicating the numeric base of generated integer output.
static const fmtflags showpoint
Generates a decimal-point character unconditionally in generated floating-point output.
static const fmtflags showpos
Generates a + sign in non-negative generated numeric output.
static const fmtflags skipws
Skips leading white space before certain input operations.
static const openmode trunc
Truncate an existing stream when opening. Default for ofstream.
static const fmtflags unitbuf
Flushes output after each output operation.
static const fmtflags uppercase
Replaces certain lowercase letters with their uppercase equivalents in generated output.

enum

void _M_cache_locale (const locale &__loc)
void _M_call_callbacks (event __ev)  throw ()
void _M_call_callbacks (event __ev)  throw ()
void _M_dispose_callbacks (void)  throw ()
__istream_type & _M_extract (_ValueT &__v)
_Words & _M_grow_words (int __index, bool __iword)
void _M_init ()  throw ()
void _M_move (ios_base &) noexcept
void _M_swap (ios_base &__rhs) noexcept
basic_istream ()
basic_istream (basic_istream &&__rhs)
basic_istream (const basic_istream &)=delete
void init (basic_streambuf< _CharT, _Traits > *__sb)
All setup is performed here.
void move (basic_ios &&__rhs)
void move (basic_ios &__rhs)
basic_istream & operator= (basic_istream &&__rhs)
basic_istream & operator= (const basic_istream &)=delete
void set_rdbuf (basic_streambuf< _CharT, _Traits > *__sb)
void swap (basic_ios &__rhs) noexcept
void swap (basic_istream &__rhs)

_Callback_list * _M_callbacks
const __ctype_type * _M_ctype
iostate _M_exception
char_type _M_fill
bool _M_fill_init
fmtflags _M_flags
streamsize _M_gcount
locale _M_ios_locale
_Words _M_local_word [_S_local_word_size]
const __num_get_type * _M_num_get
const __num_put_type * _M_num_put
streamsize _M_precision
basic_streambuf< _CharT, _Traits > * _M_streambuf
iostate _M_streambuf_state
basic_ostream< _CharT, _Traits > * _M_tie
streamsize _M_width
_Words * _M_word
int _M_word_size
_Words _M_word_zero

class std::basic_istream< _CharT, _Traits >::sentry"Performs setup work for input streams.

Objects of this class are created before all of the standard extractors are run. It is responsible for exception-safe prefix and suffix operations, although only prefix actions are currently required by the standard.

These are non-standard types.

The type of an event callback function.

Parameters

Event callbacks are user defined functions that get called during several ios_base and basic_ios functions, specifically imbue(), copyfmt(), and ~ios().

This is a bitmask type. _Ios_Iostate is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type iostate are:

• badbit
• eofbit
• failbit
• goodbit

This is a bitmask type. _Ios_Openmode is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type openmode are:

• app
• ate
• binary
• in
• out
• trunc

This is an enumerated type. _Ios_Seekdir is implementation-defined. Defined values of type seekdir are:

• beg
• cur, equivalent to SEEK_CUR in the C standard library.
• end, equivalent to SEEK_END in the C standard library.

Easy access to dependent types.

The set of events that may be passed to an event callback. erase_event is used during ~ios() and copyfmt(). imbue_event is used during imbue(). copyfmt_event is used during copyfmt().

The constructor performs all the work.

Parameters

If the stream state is good (__is.good() is true), then the following actions are performed, otherwise the sentry state is false (not okay) and failbit is set in the stream state.

The sentry's preparatory actions are:

1. if the stream is tied to an output stream, is.tie()->flush() is called to synchronize the output sequence
2. if __noskipws is false, and ios_base::skipws is set in is.flags(), the sentry extracts and discards whitespace characters from the stream. The currently imbued locale is used to determine whether each character is whitespace.

If the stream state is still good, then the sentry state becomes true (okay).

References std::ios_base::badbit, basic_istream(), std::basic_ios< _CharT, _Traits >::good(), and std::ios_base::goodbit.

Base destructor. This does very little apart from providing a virtual base dtor.

Locale access.

Returns

A reference to the current locale.

Like getloc above, but returns a reference instead of generating a copy.

Fast error checking.

Returns

True if the badbit is set.

Note that other iostate flags may also be set.

Base constructor. This ctor is almost never called by the user directly, rather from derived classes' initialization lists, which pass a pointer to their own stream buffer.

Referenced by sentry().

[Re]sets the error state.

Parameters

See std::ios_base::iostate for the possible bit values. Most users will not need to pass an argument.

Copies fields of __rhs into this.

Parameters

Returns

Reference to this object.

All fields of __rhs are copied into this object except that rdbuf() and rdstate() remain unchanged. All values in the pword and iword arrays are copied. Before copying, each callback is invoked with erase_event. After copying, each (new) callback is invoked with copyfmt_event. The final step is to copy exceptions().

Fast error checking.

Returns

True if the eofbit is set.

Note that other iostate flags may also be set.

Throwing exceptions on errors.

Returns

The current exceptions mask.

This changes nothing in the stream. See the one-argument version of exceptions(iostate) for the meaning of the return value.

Throwing exceptions on errors.

Parameters

By default, error flags are set silently. You can set an exceptions mask for each stream; if a bit in the mask becomes set in the error flags, then an exception of type std::ios_base::failure is thrown.

If the error flag is already set when the exceptions mask is added, the exception is immediately thrown. Try running the following under GCC 3.1 or later:

#include <iostream>
#include <fstream>
#include <exception>

int main()
{
    std::set_terminate (__gnu_cxx::__verbose_terminate_handler);

    std::ifstream f ("/etc/motd");

    std::cerr << "Setting badbit\n";
    f.setstate (std::ios_base::badbit);

    std::cerr << "Setting exception mask\n";
    f.exceptions (std::ios_base::badbit);
}

Fast error checking.

Returns

True if either the badbit or the failbit is set.

Checking the badbit in fail() is historical practice. Note that other iostate flags may also be set.

Retrieves the empty character.

Returns

The current fill character.

It defaults to a space (' ') in the current locale.

Sets a new empty character.

Parameters

Returns

The previous fill character.

The fill character is used to fill out space when P+ characters have been requested (e.g., via setw), Q characters are actually used, and Q<P. It defaults to a space (' ') in the current locale.

Access to format flags.

Returns

The format control flags for both input and output.

Setting new format flags all at once.

Parameters

Returns

The previous format control flags.

This function overwrites all the format flags with __fmtfl.

Character counting.

Returns

The number of characters extracted by the previous unformatted input function dispatched for this stream.

Simple extraction.

Returns

A character, or eof().

Tries to extract a character. If none are available, sets failbit and returns traits::eof().

Extraction into another streambuf.

Parameters

Returns

Returns get(__sb,widen('\n')).

Extraction into another streambuf.

Parameters

Returns

Characters are extracted and inserted into __sb until one of the following happens:

• the input sequence reaches EOF
• insertion into the output buffer fails (in this case, the character that would have been inserted is not extracted)
• the next character equals __delim (in this case, the character is not extracted)
• an exception occurs (and in this case is caught)

If no characters are stored, failbit is set in the stream's error state.

Simple extraction.

Parameters

Returns

Tries to extract a character and store it in __c. If none are available, sets failbit and returns traits::eof().

Note

This function is not overloaded on signed char and unsigned char.

Simple multiple-character extraction.

Parameters

Returns

Returns get(__s,__n,widen('\n')).

Simple multiple-character extraction.

Parameters

Returns

Characters are extracted and stored into __s until one of the following happens:

• __n-1 characters are stored
• the input sequence reaches EOF
• the next character equals __delim, in which case the character is not extracted

If no characters are stored, failbit is set in the stream's error state.

In any case, a null character is stored into the next location in the array.

Note

This function is not overloaded on signed char and unsigned char.

String extraction.

Parameters

Returns

Returns getline(__s,__n,widen('\n')).

String extraction.

Parameters

Returns

Extracts and stores characters into __s until one of the following happens. Note that these criteria are required to be tested in the order listed here, to allow an input line to exactly fill the __s array without setting failbit.

1. the input sequence reaches end-of-file, in which case eofbit is set in the stream error state
2. the next character equals __delim, in which case the character is extracted (and therefore counted in gcount()) but not stored
3. __n-1 characters are stored, in which case failbit is set in the stream error state

If no characters are extracted, failbit is set. (An empty line of input should therefore not cause failbit to be set.)

In any case, a null character is stored in the next location in the array.

Explicit specialization declarations, defined in src/istream.cc.

Explicit specialization declarations, defined in src/istream.cc.

Locale access.

Returns

A copy of the current locale.

If imbue(loc) has previously been called, then this function returns loc. Otherwise, it returns a copy of std::locale(), the global C++ locale.

Fast error checking.

Returns

True if no error flags are set.

A wrapper around rdstate.

Simple extraction.

Returns

A character, or eof().

Tries to extract a character. If none are available, sets failbit and returns traits::eof().

Simple extraction.

Returns

A character, or eof().

Tries to extract a character. If none are available, sets failbit and returns traits::eof().

Discarding characters.

Parameters

Returns

Extracts characters and throws them away until one of the following happens:

• if __n != std::numeric_limits<int>::max(), __n characters are extracted
• the input sequence reaches end-of-file
• the next character equals __delim (in this case, the character is extracted); note that this condition will never occur if __delim equals traits::eof().

NB: Provide three overloads, instead of the single function (with defaults) mandated by the Standard: this leads to a better performing implementation, while still conforming to the Standard.

Moves to a new locale.

Parameters

Returns

The previous locale.

Calls ios_base::imbue(loc), and if a stream buffer is associated with this stream, calls that buffer's pubimbue(loc).

Additional l10n notes are at https://gcc.gnu.org/onlinedocs/libstdc++/manual/localization.html

All setup is performed here. This is called from the public constructor. It is not virtual and cannot be redefined.

Access to integer array.

Parameters

Returns

A reference to an integer associated with the index.

The iword function provides access to an array of integers that can be used for any purpose. The array grows as required to hold the supplied index. All integers in the array are initialized to 0.

The implementation reserves several indices. You should use xalloc to obtain an index that is safe to use. Also note that since the array can grow dynamically, it is not safe to hold onto the reference.

Squeezes characters.

Parameters

Returns

The narrowed character.

Maps a character of char_type to a character of char, if possible.

Returns the result of

std::use_facet<ctype<char_type> >(getloc()).narrow(c,dfault)

Additional l10n notes are at https://gcc.gnu.org/onlinedocs/libstdc++/manual/localization.html

The quick-and-easy status check. This allows you to write constructs such as if (!a_stream) ... and while (a_stream) ...

Quick status checking.

Returns

The sentry state.

For ease of use, sentries may be converted to booleans. The return value is that of the sentry state (true == okay).

The quick-and-easy status check. This allows you to write constructs such as if (!a_stream) ... and while (a_stream) ...

Interface for manipulators. Manipulators such as std::ws and std::dec use these functions in constructs like std::cin >> std::ws. For more information, see the iomanip header.

Interface for manipulators. Manipulators such as std::ws and std::dec use these functions in constructs like std::cin >> std::ws. For more information, see the iomanip header.

Extracting into another streambuf.

Parameters

This function behaves like one of the basic arithmetic extractors, in that it also constructs a sentry object and has the same error handling behavior.

If __sb is NULL, the stream will set failbit in its error state.

Characters are extracted from this stream and inserted into the __sb streambuf until one of the following occurs:

• the input stream reaches end-of-file,
• insertion into the output buffer fails (in this case, the character that would have been inserted is not extracted), or
• an exception occurs (and in this case is caught)

If the function inserts no characters, failbit is set.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Floating point arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Floating point arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Interface for manipulators. Manipulators such as std::ws and std::dec use these functions in constructs like std::cin >> std::ws. For more information, see the iomanip header.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Floating point arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Integer arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Basic arithmetic extractors.

Parameters

Returns

These functions use the stream's current locale (specifically, the num_get facet) to parse the input data.

Looking ahead in the stream.

Returns

The next character, or eof().

If, after constructing the sentry object, good() is false, returns traits::eof(). Otherwise reads but does not extract the next input character.

Flags access.

Returns

The precision to generate on certain output operations.

Be careful if you try to give a definition of precision here; see DR 189.

Changing flags.

Parameters

Returns

The previous value of precision().

Unextracting a single character.

Parameters

Returns

If rdbuf() is not null, calls rdbuf()->sputbackc(c).

If rdbuf() is null or if sputbackc() fails, sets badbit in the error state.

Note

This function first clears eofbit. Since no characters are extracted, the next call to gcount() will return 0, as required by DR 60.

Access to void pointer array.

Parameters

Returns

A reference to a void* associated with the index.

The pword function provides access to an array of pointers that can be used for any purpose. The array grows as required to hold the supplied index. All pointers in the array are initialized to 0.

The implementation reserves several indices. You should use xalloc to obtain an index that is safe to use. Also note that since the array can grow dynamically, it is not safe to hold onto the reference.

Accessing the underlying buffer.

Returns

The current stream buffer.

This does not change the state of the stream.

Changing the underlying buffer.

Parameters

Returns

The previous stream buffer.

Associates a new buffer with the current stream, and clears the error state.

Due to historical accidents which the LWG refuses to correct, the I/O library suffers from a design error: this function is hidden in derived classes by overrides of the zero-argument rdbuf(), which is non-virtual for hysterical raisins. As a result, you must use explicit qualifications to access this function via any derived class. For example:

std::fstream     foo;         // or some other derived type
std::streambuf*  p = .....;

foo.ios::rdbuf(p);            // ios == basic_ios<char>

Returns the error state of the stream buffer.

Returns

A bit pattern (well, isn't everything?)

See std::ios_base::iostate for the possible bit values. Most users will call one of the interpreting wrappers, e.g., good().

Extraction without delimiters.

Parameters

Returns

If the stream state is good(), extracts characters and stores them into __s until one of the following happens:

• __n characters are stored
• the input sequence reaches end-of-file, in which case the error state is set to failbit|eofbit.

Note

This function is not overloaded on signed char and unsigned char.

Extraction until the buffer is exhausted, but no more.

Parameters

Returns

The number of characters extracted.

Extracts characters and stores them into __s depending on the number of characters remaining in the streambuf's buffer, rdbuf()->in_avail(), called A here:

• if A == -1, sets eofbit and extracts no characters
• if A == 0, extracts no characters
• if A > 0, extracts min(A,n)

The goal is to empty the current buffer, and to not request any more from the external input sequence controlled by the streambuf.

Add the callback __fn with parameter __index.

Parameters

Registers a function as an event callback with an integer parameter to be passed to the function when invoked. Multiple copies of the function are allowed. If there are multiple callbacks, they are invoked in the order they were registered.

Changing the current read position.

Parameters

Returns

If fail() is not true, calls rdbuf()->pubseekoff(__off,__dir). If that function fails, sets failbit.

Note

This function first clears eofbit. It does not count the number of characters extracted, if any, and therefore does not affect the next call to gcount().

Changing the current read position.

Parameters

Returns

If fail() is not true, calls rdbuf()->pubseekpos(__pos). If that function fails, sets failbit.

Note

This function first clears eofbit. It does not count the number of characters extracted, if any, and therefore does not affect the next call to gcount().

Setting new format flags.

Parameters

Returns

The previous format control flags.

This function sets additional flags in format control. Flags that were previously set remain set.

Setting new format flags.

Parameters

Returns

The previous format control flags.

This function clears mask in the format flags, then sets fmtfl & mask. An example mask is ios_base::adjustfield.

Sets additional flags in the error state.

Parameters

See std::ios_base::iostate for the possible bit values.

Synchronizing the stream buffer.

Returns

If rdbuf() is a null pointer, returns -1.

Otherwise, calls rdbuf()->pubsync(), and if that returns -1, sets badbit and returns -1.

Otherwise, returns 0.

Note

This function does not count the number of characters extracted, if any, and therefore does not affect the next call to gcount().

Interaction with the standard C I/O objects.

Parameters

Returns

True if the standard streams were previously synchronized.

The synchronization referred to is only that between the standard C facilities (e.g., stdout) and the standard C++ objects (e.g., cout). User-declared streams are unaffected. See https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary

Getting the current read position.

Returns

A file position object.

If fail() is not false, returns pos_type(-1) to indicate failure. Otherwise returns rdbuf()->pubseekoff(0,cur,in).

Note

This function does not count the number of characters extracted, if any, and therefore does not affect the next call to gcount(). At variance with putback, unget and seekg, eofbit is not cleared first.

Fetches the current tied stream.

Returns

A pointer to the tied stream, or NULL if the stream is not tied.

A stream may be tied (or synchronized) to a second output stream. When this stream performs any I/O, the tied stream is first flushed. For example, std::cin is tied to std::cout.

Ties this stream to an output stream.

Parameters

Returns

The previously tied output stream, or NULL if the stream was not tied.

This sets up a new tie; see tie() for more.

Unextracting the previous character.

Returns

If rdbuf() is not null, calls rdbuf()->sungetc(c).

If rdbuf() is null or if sungetc() fails, sets badbit in the error state.

Note

This function first clears eofbit. Since no characters are extracted, the next call to gcount() will return 0, as required by DR 60.

Clearing format flags.

Parameters

This function clears __mask in the format flags.

Widens characters.

Parameters

Returns

The widened character.

Maps a character of char to a character of char_type.

Returns the result of

std::use_facet<ctype<char_type> >(getloc()).widen(c)

Additional l10n notes are at https://gcc.gnu.org/onlinedocs/libstdc++/manual/localization.html

Flags access.

Returns

The minimum field width to generate on output operations.

Minimum field width refers to the number of characters.

Changing flags.

Parameters

Returns

The previous value of width().

Access to unique indices.

Returns

An integer different from all previous calls.

This function returns a unique integer every time it is called. It can be used for any purpose, but is primarily intended to be a unique index for the iword and pword functions. The expectation is that an application calls xalloc in order to obtain an index in the iword and pword arrays that can be used without fear of conflict.

The implementation maintains a static variable that is incremented and returned on each invocation. xalloc is guaranteed to return an index that is safe to use in the iword and pword arrays.

The number of characters extracted in the previous unformatted function; see gcount().

A mask of left|right|internal. Useful for the 2-arg form of setf.

Seek to end before each write.

Open and seek to end immediately after opening.

Indicates a loss of integrity in an input or output sequence (such as an irrecoverable read error from a file).

A mask of dec|oct|hex. Useful for the 2-arg form of setf.

Request a seek relative to the beginning of the stream.

Perform input and output in binary mode (as opposed to text mode). This is probably not what you think it is; see https://gcc.gnu.org/onlinedocs/libstdc++/manual/fstreams.html#std.io.filestreams.binary.

Insert/extract bool in alphabetic rather than numeric format.

Request a seek relative to the current position within the sequence.

Converts integer input or generates integer output in decimal base.

Request a seek relative to the current end of the sequence.

Indicates that an input operation reached the end of an input sequence.

Indicates that an input operation failed to read the expected characters, or that an output operation failed to generate the desired characters.

Generate floating-point output in fixed-point notation.

A mask of scientific|fixed. Useful for the 2-arg form of setf.

These are thrown to indicate problems with io. 27.4.2.1.1 Class ios_base::failure

This is a bitmask type.

_Ios_Fmtflags is implementation-defined, but it is valid to perform bitwise operations on these values and expect the Right Thing to happen. Defined objects of type fmtflags are:

• boolalpha
• dec
• fixed
• hex
• internal
• left
• oct
• right
• scientific
• showbase
• showpoint
• showpos
• skipws
• unitbuf
• uppercase
• adjustfield
• basefield
• floatfield

Indicates all is well.

Converts integer input or generates integer output in hexadecimal base.

Open for input. Default for ifstream and fstream.

Adds fill characters at a designated internal point in certain generated output, or identical to right if no such point is designated.

Adds fill characters on the right (final positions) of certain generated output. (I.e., the thing you print is flush left.)

Converts integer input or generates integer output in octal base.

Open for output. Default for ofstream and fstream.

Adds fill characters on the left (initial positions) of certain generated output. (I.e., the thing you print is flush right.)

Generates floating-point output in scientific notation.

Generates a prefix indicating the numeric base of generated integer output.

Generates a decimal-point character unconditionally in generated floating-point output.

Generates a + sign in non-negative generated numeric output.

Skips leading white space before certain input operations.

Truncate an existing stream when opening. Default for ofstream.

Flushes output after each output operation.

Replaces certain lowercase letters with their uppercase equivalents in generated output.