std::basic_filebuf<CharT,Traits>::pbackfail
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basic_filebuf::pbackfail
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protected:
virtual int_type pbackfail( int_type c = Traits::eof() )
virtual int_type pbackfail( int_type c = Traits::eof() )
This protected virtual function is called by the public functions basic_streambuf::sungetc and basic_streambuf::sputbackc (which, in turn, are called by basic_istream::unget and basic_istream::putback).
1) The caller is requesting that the get area is backed up by one character (
pbackfail()
is called with no arguments), in which case, this function re-reads the file starting one byte earlier and decrements basic_streambuf::gptr(), e.g. by calling gbump(-1).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 which casea) First, checks if there is a putback position, and if there isn't, backs up the get area by re-reading the file starting one byte earlier.
a) Then checks what character is in the putback position. If the character held there is already equal to
c
, as determined by Traits::eq(to_char_type(c), gptr()[-1]), then simply decrements basic_streambuf::gptr().b) Otherwise, if the buffer is allowed to modify its own get area, decrements basic_streambuf::gptr() and writes
c
to the location pointed to gptr() after adjustment.This function never modifies the file, only the get area of the in-memory buffer.
If the file is not open (is_open()==false, this function returns Traits::eof() immediately.
Contents
[edit] Parameters
c
-
the character to put back, or Traits::eof() to indicate that backing up of the get area is requested
[edit] Return value
c on success except if c
was Traits::eof(), in which case Traits::not_eof(c) is returned.
Traits::eof() on failure.
[edit] Example
This section is incomplete
Reason: no example
Reason: no example
[edit] See also
[virtual]
(virtual protected member function of
std::basic_streambuf<CharT,Traits>
) [edit]
moves the next pointer in the input sequence back by one
(public member function of
(public member function of
std::basic_streambuf<CharT,Traits>
) [edit]
puts one character back in the input sequence
(public member function of
(public member function of
std::basic_streambuf<CharT,Traits>
) [edit]