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).
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).
pbackfail()is called with the character that needs to be put back), in which case
c, as determined by Traits::eq(to_char_type(c), gptr()[-1]), then simply decrements basic_streambuf::gptr().
cto 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.
|c||-||the character to put back, or Traits::eof() to indicate that backing up of the get area is requested|
c on success except if
c was Traits::eof(), in which case Traits::not_eof(c) is returned.
Traits::eof() on failure.
|This section is incomplete|
Reason: no example