std::basic_streambuf::pbackfail

 

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Technical Specifications

 

Input/output library

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basic_streambuf

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basic_osyncstream (C++20)

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std::basic_streambuf

Public member functions

basic_streambuf::~basic_streambuf

Locales

basic_streambuf::pubimbue

basic_streambuf::getloc

Positioning

basic_streambuf::pubsetbuf

basic_streambuf::pubseekoff

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Get area

basic_streambuf::in_avail

basic_streambuf::snextc

basic_streambuf::sbumpc

basic_streambuf::sgetc

basic_streambuf::sgetn

Put area

basic_streambuf::sputc

basic_streambuf::sputn

Putback

basic_streambuf::sputbackc

basic_streambuf::sungetc

Protected member functions

basic_streambuf::basic_streambuf

basic_streambuf::operator= (C++11)

basic_streambuf::swap (C++11)

Locales

basic_streambuf::imbue

Positioning

basic_streambuf::setbuf

basic_streambuf::seekoff

basic_streambuf::seekpos

basic_streambuf::sync

Get area

basic_streambuf::showmanyc

basic_streambuf::underflow

basic_streambuf::uflow

basic_streambuf::xsgetn

basic_streambuf::ebackbasic_streambuf::gptrbasic_streambuf::egptr

basic_streambuf::gbump

basic_streambuf::setg

Put area

basic_streambuf::xsputn

basic_streambuf::overflow

basic_streambuf::pbasebasic_streambuf::pptrbasic_streambuf::epptr

basic_streambuf::pbump

basic_streambuf::setp

Putback

basic_streambuf::pbackfail

 

protected: virtual int_type pbackfail( int_type c = Traits::eof() );

This protected virtual function is called by the public functions sungetc() and sputbackc() (which, in turn, are called by basic_istream::unget and basic_istream::putback) when either:

1) There is no putback position in the get area (pbackfail() is called with no arguments). In this situation, the purpose of pbackfail() is to back up the get area by one character, if the associated character sequence allows this (e.g. a file-backed streambuf may reload the buffer from a file, starting one character earlier).

2) The caller attempts to putback a different character from the one retrieved earlier (pbackfail() is called with the character that needs to be put back). In this situation, the purpose of pbackfail() is to place the character c into the get area at the position just before basic_streambuf::gptr(), and, if possible, to modify the associated character sequence to reflect this change. This may involve backing up the get area as in the first variant.

The default base class version of this function does nothing and returns Traits::eof() in all situations. This function is overridden by the derived classes: basic_stringbuf::pbackfail, basic_filebuf::pbackfail, strstreambuf::pbackfail, and is expected to be overridden by user-defined and third-party library stream classes.

Parameters

ch

-

character to put back or Traits::eof() if only back out is requested

Return value

Traits::eof() in case of failure, some other value to indicate success. The base class version always fails.

See also

pbackfail [virtual]	backs out the input sequence to unget a character, not affecting the associated file (virtual protected member function of std::basic_filebuf)
pbackfail [virtual]	puts a character back into the input sequence (virtual protected member function of std::basic_stringbuf)
pbackfail [virtual]	backs out the input sequence to unget a character (virtual protected member function of std::strstreambuf)
sungetc	moves the next pointer in the input sequence back by one (public member function)
sputbackc	puts one character back in the input sequence (public member function)