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std::basic_stringbuf::pbackfail

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< cpp‎ | io‎ | basic stringbuf
Revision as of 11:11, 9 December 2012 by Cubbi (Talk | contribs)

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 or with Traits::eof() as the argument)
a) First, checks if there is a putback position, and if there really isn't, fails. (stringbuf has no external character source to re-read)
b) If the caller was wrong and the putback position is in fact available, simply 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, fails.
b) 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().
c) Otherwise, if the buffer is open for reading only, fails.
d) Otherwise, if the buffer is open for writing (mode && std::ios_base::out is nonzero), then decrements basic_streambuf::gptr() and writes c to the location pointed to gptr() after adjustment.

Contents

Parameters

c - the character to put back, or Traits::eof() to indicate that backing up of the get area is requested

Return value

c on success except if c was Traits::eof(), in which case Traits::not_eof(c) is returned.

Traits::eof() on failure.

Example

See also

Template:cpp/io/basic streambuf/dcl list pbackfailTemplate:cpp/io/basic streambuf/dcl list sungetcTemplate:cpp/io/basic streambuf/dcl list sputbackcTemplate:cpp/io/basic istream/dcl list ungetTemplate:cpp/io/basic istream/dcl list putback