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/*
* Copyright (c) 1990 The Regents of the University of California.
* All rights reserved.
*
* Redistribution and use in source and binary forms are permitted
* provided that the above copyright notice and this paragraph are
* duplicated in all such forms and that any documentation,
* advertising materials, and other materials related to such
* distribution and use acknowledge that the software was developed
* by the University of California, Berkeley. The name of the
* University may not be used to endorse or promote products derived
* from this software without specific prior written permission.
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
* WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
*/
/*
FUNCTION
<<ftell>>---return position in a stream or file
INDEX
ftell
ANSI_SYNOPSIS
#include <stdio.h>
long ftell(FILE *<[fp]>);
TRAD_SYNOPSIS
#include <stdio.h>
long ftell(<[fp]>)
FILE *<[fp]>;
DESCRIPTION
Objects of type <<FILE>> can have a ``position'' that records how much
of the file your program has already read. Many of the <<stdio>> functions
depend on this position, and many change it as a side effect.
The result of <<ftell>> is the current position for a file
identified by <[fp]>. If you record this result, you can later
use it with <<fseek>> to return the file to this
position.
In the current implementation, <<ftell>> simply uses a character
count to represent the file position; this is the same number that
would be recorded by <<fgetpos>>.
RETURNS
<<ftell>> returns the file position, if possible. If it cannot do
this, it returns <<-1L>>. Failure occurs on streams that do not support
positioning; the global <<errno>> indicates this condition with the
value <<ESPIPE>>.
PORTABILITY
<<ftell>> is required by the ANSI C standard, but the meaning of its
result (when successful) is not specified beyond requiring that it be
acceptable as an argument to <<fseek>>. In particular, other
conforming C implementations may return a different result from
<<ftell>> than what <<fgetpos>> records.
No supporting OS subroutines are required.
*/
#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "%W% (Berkeley) %G%";
#endif /* LIBC_SCCS and not lint */
/*
* ftell: return current offset.
*/
#include <stdio.h>
#include <errno.h>
#include "local.h"
long
_DEFUN (ftell, (fp),
register FILE * fp)
{
fpos_t pos;
/* Ensure stdio is set up. */
CHECK_INIT (fp);
if (fp->_seek == NULL)
{
fp->_data->_errno = ESPIPE;
return -1L;
}
/* Find offset of underlying I/O object, then
adjust for buffered bytes. */
fflush(fp); /* may adjust seek offset on append stream */
if (fp->_flags & __SOFF)
pos = fp->_offset;
else
{
pos = (*fp->_seek) (fp->_cookie, (fpos_t) 0, SEEK_CUR);
if (pos == -1L)
return pos;
}
if (fp->_flags & __SRD)
{
/*
* Reading. Any unread characters (including
* those from ungetc) cause the position to be
* smaller than that in the underlying object.
*/
pos -= fp->_r;
if (HASUB (fp))
pos -= fp->_ur;
}
else if (fp->_flags & __SWR && fp->_p != NULL)
{
/*
* Writing. Any buffered characters cause the
* position to be greater than that in the
* underlying object.
*/
pos += fp->_p - fp->_bf._base;
}
return pos;
}
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