newlib/libc/stdio/ftell.c

   1 /*
   2  * Copyright (c) 1990 The Regents of the University of California.
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms are permitted
   6  * provided that the above copyright notice and this paragraph are
   7  * duplicated in all such forms and that any documentation,
   8  * and/or other materials related to such
   9  * distribution and use acknowledge that the software was developed
  10  * by the University of California, Berkeley.  The name of the
  11  * University may not be used to endorse or promote products derived
  12  * from this software without specific prior written permission.
  13  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
  14  * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
  15  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  16  */
  17
  18 /*
  19 FUNCTION
  20 <<ftell>>, <<ftello>>---return position in a stream or file
  21
  22 INDEX
  23         ftell
  24 INDEX
  25         ftello
  26 INDEX
  27         _ftell_r
  28 INDEX
  29         _ftello_r
  30
  31 SYNOPSIS
  32         #include <stdio.h>
  33         long ftell(FILE *<[fp]>);
  34         off_t ftello(FILE *<[fp]>);
  35         long _ftell_r(struct _reent *<[ptr]>, FILE *<[fp]>);
  36         off_t _ftello_r(struct _reent *<[ptr]>, FILE *<[fp]>);
  37
  38 DESCRIPTION
  39 Objects of type <<FILE>> can have a ``position'' that records how much
  40 of the file your program has already read.  Many of the <<stdio>> functions
  41 depend on this position, and many change it as a side effect.
  42
  43 The result of <<ftell>>/<<ftello>> is the current position for a file
  44 identified by <[fp]>.  If you record this result, you can later
  45 use it with <<fseek>>/<<fseeko>> to return the file to this
  46 position.  The difference between <<ftell>> and <<ftello>> is that
  47 <<ftell>> returns <<long>> and <<ftello>> returns <<off_t>>.
  48
  49 In the current implementation, <<ftell>>/<<ftello>> simply uses a character
  50 count to represent the file position; this is the same number that
  51 would be recorded by <<fgetpos>>.
  52
  53 RETURNS
  54 <<ftell>>/<<ftello>> return the file position, if possible.  If they cannot do
  55 this, they return <<-1L>>.  Failure occurs on streams that do not support
  56 positioning; the global <<errno>> indicates this condition with the
  57 value <<ESPIPE>>.
  58
  59 PORTABILITY
  60 <<ftell>> is required by the ANSI C standard, but the meaning of its
  61 result (when successful) is not specified beyond requiring that it be
  62 acceptable as an argument to <<fseek>>.  In particular, other
  63 conforming C implementations may return a different result from
  64 <<ftell>> than what <<fgetpos>> records.
  65
  66 <<ftello>> is defined by the Single Unix specification.
  67
  68 No supporting OS subroutines are required.
  69 */
  70
  71 #if defined(LIBC_SCCS) && !defined(lint)
  72 static char sccsid[] = "%W% (Berkeley) %G%";
  73 #endif /* LIBC_SCCS and not lint */
  74
  75 /*
  76  * ftell: return current offset.
  77  */
  78
  79 #include <_ansi.h>
  80 #include <reent.h>
  81 #include <stdio.h>
  82 #include <errno.h>
  83 #include "local.h"
  84
  85 long
  86 _ftell_r (struct _reent *ptr,
  87        register FILE * fp)
  88 {
  89   _fpos_t pos;
  90
  91   pos = _ftello_r (ptr, fp);
  92   if ((long)pos != pos)
  93     {
  94       pos = -1;
  95       _REENT_ERRNO(ptr) = EOVERFLOW;
  96     }
  97   return (long)pos;
  98 }
  99
 100 #ifndef _REENT_ONLY
 101
 102 long
 103 ftell (register FILE * fp)
 104 {
 105   return _ftell_r (_REENT, fp);
 106 }
 107
 108 #endif /* !_REENT_ONLY */