man3/fseeko.3

   1 .\" Copyright 2001 Andries Brouwer <aeb@cwi.nl>.
   2 .\"
   3 .\" SPDX-License-Identifier: Linux-man-pages-copyleft
   4 .\"
   5 .TH FSEEKO 3 2021-03-22 GNU "Linux Programmer's Manual"
   6 .SH NAME
   7 fseeko, ftello \- seek to or report file position
   8 .SH LIBRARY
   9 Standard C library
  10 .RI ( libc ", " \-lc )
  11 .SH SYNOPSIS
  12 .nf
  13 .B #include <stdio.h>
  14 .PP
  15 .BI "int fseeko(FILE *" stream ", off_t " offset ", int " whence );
  16 .BI "off_t ftello(FILE *" stream );
  17 .fi
  18 .PP
  19 .RS -4
  20 Feature Test Macro Requirements for glibc (see
  21 .BR feature_test_macros (7)):
  22 .RE
  23 .PP
  24 .BR fseeko (),
  25 .BR ftello ():
  26 .nf
  27     _FILE_OFFSET_BITS == 64 || _POSIX_C_SOURCE >= 200112L
  28 .fi
  29 .SH DESCRIPTION
  30 The
  31 .BR fseeko ()
  32 and
  33 .BR ftello ()
  34 functions are identical to
  35 .BR fseek (3)
  36 and
  37 .BR ftell (3)
  38 (see
  39 .BR fseek (3)),
  40 respectively, except that the
  41 .I offset
  42 argument of
  43 .BR fseeko ()
  44 and the return value of
  45 .BR ftello ()
  46 is of type
  47 .I off_t
  48 instead of
  49 .IR long .
  50 .PP
  51 On some architectures, both
  52 .I off_t
  53 and
  54 .I long
  55 are 32-bit types, but defining
  56 .B _FILE_OFFSET_BITS
  57 with the value 64 (before including
  58 .I any
  59 header files)
  60 will turn
  61 .I off_t
  62 into a 64-bit type.
  63 .SH RETURN VALUE
  64 On successful completion,
  65 .BR fseeko ()
  66 returns 0, while
  67 .BR ftello ()
  68 returns the current offset.
  69 Otherwise, \-1 is returned and
  70 .I errno
  71 is set to indicate the error.
  72 .SH ERRORS
  73 See the ERRORS in
  74 .BR fseek (3).
  75 .SH VERSIONS
  76 These functions are available under glibc since version 2.1.
  77 .SH ATTRIBUTES
  78 For an explanation of the terms used in this section, see
  79 .BR attributes (7).
  80 .ad l
  81 .nh
  82 .TS
  83 allbox;
  84 lbx lb lb
  85 l l l.
  86 Interface       Attribute       Value
  87 T{
  88 .BR fseeko (),
  89 .BR ftello ()
  90 T}      Thread safety   MT-Safe
  91 .TE
  92 .hy
  93 .ad
  94 .sp 1
  95 .SH CONFORMING TO
  96 POSIX.1-2001, POSIX.1-2008, SUSv2.
  97 .SH NOTES
  98 The declarations of these functions can also be obtained by defining
  99 the obsolete
 100 .B _LARGEFILE_SOURCE
 101 feature test macro.
 102 .SH SEE ALSO
 103 .BR fseek (3)