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