newlib/libc/stdio/ftello.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  * ftello: 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 _off_t
  86 _ftello_r (struct _reent * ptr,
  87        register FILE * fp)
  88 {
  89   _fpos_t pos;
  90
  91   /* Ensure stdio is set up.  */
  92
  93   CHECK_INIT (ptr, fp);
  94
  95   _newlib_flockfile_start (fp);
  96
  97   if (fp->_seek == NULL)
  98     {
  99       _REENT_ERRNO(ptr) = ESPIPE;
 100       _newlib_flockfile_exit (fp);
 101       return (_off_t) -1;
 102     }
 103
 104   /* Find offset of underlying I/O object, then adjust for buffered bytes. */
 105   if (!(fp->_flags & __SRD) && (fp->_flags & __SWR) &&
 106       fp->_p != NULL && fp->_p - fp->_bf._base > 0 &&
 107       (fp->_flags & __SAPP))
 108     {
 109       pos = fp->_seek (ptr, fp->_cookie, (_fpos_t) 0, SEEK_END);
 110       if (pos == (_fpos_t) -1)
 111         {
 112           _newlib_flockfile_exit (fp);
 113           return (_off_t) -1;
 114         }
 115     }
 116   else if (fp->_flags & __SOFF)
 117     pos = fp->_offset;
 118   else
 119     {
 120       pos = fp->_seek (ptr, fp->_cookie, (_fpos_t) 0, SEEK_CUR);
 121       if (pos == (_fpos_t) -1)
 122         {
 123           _newlib_flockfile_exit (fp);
 124           return (_off_t) -1;
 125         }
 126     }
 127   if (fp->_flags & __SRD)
 128     {
 129       /*
 130        * Reading.  Any unread characters (including
 131        * those from ungetc) cause the position to be
 132        * smaller than that in the underlying object.
 133        */
 134       pos -= fp->_r;
 135       if (HASUB (fp))
 136         pos -= fp->_ur;
 137     }
 138   else if ((fp->_flags & __SWR) && fp->_p != NULL)
 139     {
 140       /*
 141        * Writing.  Any buffered characters cause the
 142        * position to be greater than that in the
 143        * underlying object.
 144        */
 145       pos += fp->_p - fp->_bf._base;
 146     }
 147
 148   _newlib_flockfile_end (fp);
 149   return (_off_t) pos;
 150 }
 151
 152 #ifndef _REENT_ONLY
 153
 154 _off_t
 155 ftello (register FILE * fp)
 156 {
 157   return _ftello_r (_REENT, fp);
 158 }
 159
 160 #endif /* !_REENT_ONLY */