protected:
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 case
a) 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.
[edit] Parameters c - the character to put back, or Traits::eof() to indicate that backing up of the get area is requested [edit] Return valuec on success except if c was Traits::eof(), in which case Traits::not_eof(c) is returned.
Traits::eof() on failure.
[edit] Example [edit] See also puts a character back into the input sequence, possibly modifying the input sequencestd::basic_streambuf<CharT,Traits>) [edit] moves the next pointer in the input sequence back by one
std::basic_streambuf<CharT,Traits>) [edit] puts one character back in the input sequence
std::basic_streambuf<CharT,Traits>) [edit] unextracts a character
std::basic_istream<CharT,Traits>) [edit] puts a character into input stream
std::basic_istream<CharT,Traits>) [edit]
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