lib/libc/stdio/ftell.c

   1 /*      $NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos 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. Neither the name of the University nor the names of its contributors
  19  *    may be used to endorse or promote products derived from this software
  20  *    without specific prior written permission.
  21  *
  22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  32  * SUCH DAMAGE.
  33  */
  34
  35 #include <sys/cdefs.h>
  36 #if defined(LIBC_SCCS) && !defined(lint)
  37 #if 0
  38 static char sccsid[] = "@(#)ftell.c     8.2 (Berkeley) 5/4/95";
  39 #else
  40 __RCSID("$NetBSD: ftell.c,v 1.20 2012/03/27 15:05:42 christos Exp $");
  41 #endif
  42 #endif /* LIBC_SCCS and not lint */
  43
  44 #include <assert.h>
  45 #include <errno.h>
  46 #include <stdio.h>
  47 #include "reentrant.h"
  48 #include "local.h"
  49
  50 /*
  51  * ftell: return current offset.
  52  */
  53 long
  54 ftell(FILE *fp)
  55 {
  56         off_t pos;
  57
  58
  59         FLOCKFILE(fp);
  60
  61         if (fp->_seek == NULL) {
  62                 FUNLOCKFILE(fp);
  63                 errno = ESPIPE;                 /* historic practice */
  64                 return -1L;
  65         }
  66
  67         /*
  68          * Find offset of underlying I/O object, then
  69          * adjust for buffered bytes.
  70          */
  71         (void)__sflush(fp); /* may adjust seek offset on append stream */
  72         if (fp->_flags & __SOFF)
  73                 pos = fp->_offset;
  74         else {
  75                 pos = (*fp->_seek)(fp->_cookie, (off_t)0, SEEK_CUR);
  76                 if (pos == -1L) {
  77                         FUNLOCKFILE(fp);
  78                         return (long)pos;
  79                 }
  80         }
  81         if (fp->_flags & __SRD) {
  82                 /*
  83                  * Reading.  Any unread characters (including
  84                  * those from ungetc) cause the position to be
  85                  * smaller than that in the underlying object.
  86                  */
  87                 pos -= fp->_r;
  88                 if (HASUB(fp))
  89                         pos -= fp->_ur;
  90         } else if (fp->_flags & __SWR && fp->_p != NULL) {
  91                 /*
  92                  * Writing.  Any buffered characters cause the
  93                  * position to be greater than that in the
  94                  * underlying object.
  95                  */
  96                 pos += fp->_p - fp->_bf._base;
  97         }
  98         FUNLOCKFILE(fp);
  99
 100         if (__long_overflow(pos)) {
 101                 errno = EOVERFLOW;
 102                 return -1L;
 103         }
 104
 105         return (long)pos;
 106 }