toolchain/gcc/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  * advertising materials, and 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 ANSI_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 TRAD_SYNOPSIS
  39         #include <stdio.h>
  40         long ftell(<[fp]>)
  41         FILE *<[fp]>;
  42
  43         off_t ftello(<[fp]>)
  44         FILE *<[fp]>;
  45
  46         long _ftell_r(<[ptr]>, <[fp]>)
  47         struct _reent *<[ptr]>;
  48         FILE *<[fp]>;
  49
  50         off_t _ftello_r(<[ptr]>, <[fp]>)
  51         struct _reent *<[ptr]>;
  52         FILE *<[fp]>;
  53
  54 DESCRIPTION
  55 Objects of type <<FILE>> can have a ``position'' that records how much
  56 of the file your program has already read.  Many of the <<stdio>> functions
  57 depend on this position, and many change it as a side effect.
  58
  59 The result of <<ftell>>/<<ftello>> is the current position for a file
  60 identified by <[fp]>.  If you record this result, you can later
  61 use it with <<fseek>>/<<fseeko>> to return the file to this
  62 position.  The difference between <<ftell>> and <<ftello>> is that
  63 <<ftell>> returns <<long>> and <<ftello>> returns <<off_t>>.
  64
  65 In the current implementation, <<ftell>>/<<ftello>> simply uses a character
  66 count to represent the file position; this is the same number that
  67 would be recorded by <<fgetpos>>.
  68
  69 RETURNS
  70 <<ftell>>/<<ftello>> return the file position, if possible.  If they cannot do
  71 this, they return <<-1L>>.  Failure occurs on streams that do not support
  72 positioning; the global <<errno>> indicates this condition with the
  73 value <<ESPIPE>>.
  74
  75 PORTABILITY
  76 <<ftell>> is required by the ANSI C standard, but the meaning of its
  77 result (when successful) is not specified beyond requiring that it be
  78 acceptable as an argument to <<fseek>>.  In particular, other
  79 conforming C implementations may return a different result from
  80 <<ftell>> than what <<fgetpos>> records.
  81
  82 <<ftello>> is defined by the Single Unix specification.
  83
  84 No supporting OS subroutines are required.
  85 */
  86
  87 #if defined(LIBC_SCCS) && !defined(lint)
  88 static char sccsid[] = "%W% (Berkeley) %G%";
  89 #endif /* LIBC_SCCS and not lint */
  90
  91 /*
  92  * ftell: return current offset.
  93  */
  94
  95 #include <stdio.h>
  96 #include <errno.h>
  97
  98 #include "local.h"
  99
 100 long
 101 _DEFUN (_ftell_r, (ptr, fp),
 102         struct _reent *ptr _AND
 103         register FILE * fp)
 104 {
 105   _fpos_t pos;
 106
 107   _flockfile(fp);
 108
 109   /* Ensure stdio is set up.  */
 110
 111   CHECK_INIT (fp);
 112
 113   if (fp->_seek == NULL)
 114     {
 115       ptr->_errno = ESPIPE;
 116       _funlockfile(fp);
 117       return -1L;
 118     }
 119
 120   /* Find offset of underlying I/O object, then
 121      adjust for buffered bytes.  */
 122   fflush(fp);           /* may adjust seek offset on append stream */
 123   if (fp->_flags & __SOFF)
 124     pos = fp->_offset;
 125   else
 126     {
 127       pos = (*fp->_seek) (fp->_cookie, (_fpos_t) 0, SEEK_CUR);
 128       if (pos == -1L)
 129         {
 130           _funlockfile(fp);
 131           return pos;
 132         }
 133     }
 134   if (fp->_flags & __SRD)
 135     {
 136       /*
 137        * Reading.  Any unread characters (including
 138        * those from ungetc) cause the position to be
 139        * smaller than that in the underlying object.
 140        */
 141       pos -= fp->_r;
 142       if (HASUB (fp))
 143         pos -= fp->_ur;
 144     }
 145   else if (fp->_flags & __SWR && fp->_p != NULL)
 146     {
 147       /*
 148        * Writing.  Any buffered characters cause the
 149        * position to be greater than that in the
 150        * underlying object.
 151        */
 152       pos += fp->_p - fp->_bf._base;
 153     }
 154
 155   _funlockfile(fp);
 156   return pos;
 157 }
 158
 159 #ifndef _REENT_ONLY
 160
 161 long
 162 _DEFUN (ftell, (fp),
 163         register FILE * fp)
 164 {
 165   return _ftell_r (_REENT, fp);
 166 }
 167
 168 #endif /* !_REENT_ONLY */