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sortix--sortix/libc/stdio/ftello_unlocked.cpp

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/*******************************************************************************
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Copyright(C) Jonas 'Sortie' Termansen 2011, 2012, 2013, 2014.
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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/>.
stdio/ftello_unlocked.cpp
Returns the current offset of a FILE.
*******************************************************************************/
#include <sys/types.h>
#include <errno.h>
#include <stdio.h>
extern "C" off_t ftello_unlocked(FILE* fp)
{
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if ( !fp->seek_func )
return errno = EBADF, fp->flags |= _FILE_STATUS_ERROR, -1;
off_t offset = fp->seek_func(fp->user, 0, SEEK_CUR);
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if ( offset < 0 )
return -1;
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off_t read_ahead = fp->amount_input_buffered - fp->offset_input_buffer;
off_t write_behind = fp->amount_output_buffered;
if ( offset < read_ahead + write_behind ) // Too much ungetc'ing.
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return 0;
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return offset - read_ahead + write_behind;
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}