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ftell.c revision 1.12 
      1 /*	$NetBSD: ftell.c,v 1.12 1999/09/16 11:45:28 lukem Exp $	*/
      2 
      3 /*-
      4  * Copyright (c) 1990, 1993
      5  *	The Regents of the University of California.  All rights reserved.
      6  *
      7  * This code is derived from software contributed to Berkeley by
      8  * Chris Torek.
      9  *
     10  * Redistribution and use in source and binary forms, with or without
     11  * modification, are permitted provided that the following conditions
     12  * are met:
     13  * 1. Redistributions of source code must retain the above copyright
     14  *    notice, this list of conditions and the following disclaimer.
     15  * 2. Redistributions in binary form must reproduce the above copyright
     16  *    notice, this list of conditions and the following disclaimer in the
     17  *    documentation and/or other materials provided with the distribution.
     18  * 3. All advertising materials mentioning features or use of this software
     19  *    must display the following acknowledgement:
     20  *	This product includes software developed by the University of
     21  *	California, Berkeley and its contributors.
     22  * 4. Neither the name of the University nor the names of its contributors
     23  *    may be used to endorse or promote products derived from this software
     24  *    without specific prior written permission.
     25  *
     26  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
     27  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
     28  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
     29  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
     30  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
     31  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
     32  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
     33  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
     34  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     35  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     36  * SUCH DAMAGE.
     37  */
     38 
     39 #include <sys/cdefs.h>
     40 #if defined(LIBC_SCCS) && !defined(lint)
     41 #if 0
     42 static char sccsid[] = "@(#)ftell.c	8.2 (Berkeley) 5/4/95";
     43 #else
     44 __RCSID("$NetBSD: ftell.c,v 1.12 1999/09/16 11:45:28 lukem Exp $");
     45 #endif
     46 #endif /* LIBC_SCCS and not lint */
     47 
     48 #include <assert.h>
     49 #include <errno.h>
     50 #include <stdio.h>
     51 #include "local.h"
     52 #include "reentrant.h"
     53 
     54 /*
     55  * ftell: return current offset.
     56  */
     57 long
     58 ftell(fp)
     59 	FILE *fp;
     60 {
     61 	fpos_t pos;
     62 
     63 #ifdef _DIAGNOSTIC
     64 	_DIAGASSERT(fp != NULL);
     65 	if (fp == NULL) {
     66 		errno = EBADF;
     67 		return (-1);
     68 	}
     69 #endif
     70 
     71 	FLOCKFILE(fp);
     72 
     73 	if (fp->_seek == NULL) {
     74 		FUNLOCKFILE(fp);
     75 		errno = ESPIPE;			/* historic practice */
     76 		return (-1L);
     77 	}
     78 
     79 	/*
     80 	 * Find offset of underlying I/O object, then
     81 	 * adjust for buffered bytes.
     82 	 */
     83 	__sflush(fp);		/* may adjust seek offset on append stream */
     84 	if (fp->_flags & __SOFF)
     85 		pos = fp->_offset;
     86 	else {
     87 		pos = (*fp->_seek)(fp->_cookie, (fpos_t)0, SEEK_CUR);
     88 		if (pos == -1L) {
     89 			FUNLOCKFILE(fp);
     90 			return (long)(pos);
     91 		}
     92 	}
     93 	if (fp->_flags & __SRD) {
     94 		/*
     95 		 * Reading.  Any unread characters (including
     96 		 * those from ungetc) cause the position to be
     97 		 * smaller than that in the underlying object.
     98 		 */
     99 		pos -= fp->_r;
    100 		if (HASUB(fp))
    101 			pos -= fp->_ur;
    102 	} else if (fp->_flags & __SWR && fp->_p != NULL) {
    103 		/*
    104 		 * Writing.  Any buffered characters cause the
    105 		 * position to be greater than that in the
    106 		 * underlying object.
    107 		 */
    108 		pos += fp->_p - fp->_bf._base;
    109 	}
    110 	FUNLOCKFILE(fp);
    111 	return (long)(pos);
    112 }
    113