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( FILE *<[fp]>);
36 off_t ftello( 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 #define _DEFAULT_SOURCE
80 #include <_ansi.h>
81 #include <stdio.h>
82 #include <errno.h>
83 #include "local.h"
84
85 long
ftell(register FILE * fp)86 ftell (
87 register FILE * fp)
88 {
89 _fpos_t pos;
90
91 pos = ftello ( fp);
92 if ((long)pos != pos)
93 {
94 pos = -1;
95 _REENT_ERRNO(ptr) = EOVERFLOW;
96 }
97 return (long)pos;
98 }
99
