lib/libc/stdio/ftello.c

   1 /*      $NetBSD: ftello.c,v 1.7 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 __RCSID("$NetBSD: ftello.c,v 1.7 2012/03/27 15:05:42 christos Exp $");
  38 #endif /* LIBC_SCCS and not lint */
  39
  40 #include "namespace.h"
  41 #include <assert.h>
  42 #include <errno.h>
  43 #include <stdio.h>
  44 #include "reentrant.h"
  45 #include "local.h"
  46
  47 #ifdef __weak_alias
  48 __weak_alias(ftello, _ftello)
  49 #endif
  50
  51 /*
  52  * ftell: return current offset.
  53  */
  54 off_t
  55 ftello(FILE *fp)
  56 {
  57         off_t pos;
  58
  59
  60         FLOCKFILE(fp);
  61
  62         if (fp->_seek == NULL) {
  63                 FUNLOCKFILE(fp);
  64                 errno = ESPIPE;                 /* historic practice */
  65                 return (off_t)-1;
  66         }
  67
  68         /*
  69          * Find offset of underlying I/O object, then
  70          * adjust for buffered bytes.
  71          */
  72         (void)__sflush(fp); /* may adjust seek offset on append stream */
  73         if (fp->_flags & __SOFF)
  74                 pos = fp->_offset;
  75         else {
  76                 pos = (*fp->_seek)(fp->_cookie, (off_t)0, SEEK_CUR);
  77                 if (pos == (off_t)-1) {
  78                         FUNLOCKFILE(fp);
  79                         return pos;
  80                 }
  81         }
  82         if (fp->_flags & __SRD) {
  83                 /*
  84                  * Reading.  Any unread characters (including
  85                  * those from ungetc) cause the position to be
  86                  * smaller than that in the underlying object.
  87                  */
  88                 pos -= fp->_r;
  89                 if (HASUB(fp))
  90                         pos -= fp->_ur;
  91         } else if (fp->_flags & __SWR && fp->_p != NULL) {
  92                 /*
  93                  * Writing.  Any buffered characters cause the
  94                  * position to be greater than that in the
  95                  * underlying object.
  96                  */
  97                 pos += fp->_p - fp->_bf._base;
  98         }
  99         FUNLOCKFILE(fp);
 100         return pos;
 101 }