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sortix--sortix/libc/ftello.cpp

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/*******************************************************************************
Copyright(C) Jonas 'Sortie' Termansen 2011, 2012.
This file is part of the Sortix C Library.
The Sortix C Library is free software: you can redistribute it and/or modify
it under the terms of the GNU Lesser General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at your
option) any later version.
The Sortix C Library is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public
License for more details.
You should have received a copy of the GNU Lesser General Public License
along with the Sortix C Library. If not, see <http://www.gnu.org/licenses/>.
ftello.cpp
Returns the current offset of a FILE.
*******************************************************************************/
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
extern "C" off_t ftello(FILE* fp)
{
if ( !fp->tell_func )
return errno = EBADF, -1;
off_t offset = fp->tell_func(fp->user);
if ( offset < 0 )
return -1;
off_t readahead = fp->amount_input_buffered - fp->offset_input_buffer;
off_t writebehind = fp->amount_output_buffered;
off_t result = offset - readahead + writebehind;
if ( result < 0 ) // Too much ungetc'ing.
return 0;
return result;
}