FSEEK
Section: Linux Programmer's Manual (3)
Updated: 2018-04-30
Page Index
NAME
fgetpos, fseek, fsetpos, ftell, rewind - reposition a stream
SYNOPSIS
#include <stdio.h>
int fseek(FILE *stream, long offset, int whence);
long ftell(FILE *stream);
void rewind(FILE *stream);
int fgetpos(FILE *stream, fpos_t *pos);
int fsetpos(FILE *stream, const fpos_t *pos);
DESCRIPTION
The
fseek()
function sets the file position indicator for the stream pointed to by
stream.
The new position, measured in bytes, is obtained by adding
offset
bytes to the position specified by
whence.
If
whence
is set to
SEEK_SET,
SEEK_CUR,
or
SEEK_END,
the offset is relative to the start of the file, the current position
indicator, or end-of-file, respectively.
A successful call to the
fseek()
function clears the end-of-file indicator for the stream and undoes
any effects of the
ungetc(3)
function on the same stream.
The
ftell()
function obtains the current value of the file position indicator for the
stream pointed to by
stream.
The
rewind()
function sets the file position indicator for the stream pointed to by
stream
to the beginning of the file.
It is equivalent to:
-
(void) fseek(stream, 0L, SEEK_SET)
except that the error indicator for the stream is also cleared (see
clearerr(3)).
The
fgetpos()
and
fsetpos()
functions are alternate interfaces equivalent to
ftell()
and
fseek()
(with
whence
set to
SEEK_SET),
setting and storing the current value of the file offset into or from the
object referenced by
pos.
On some non-UNIX systems, an
fpos_t
object may be a complex object and these routines may be the only way to
portably reposition a text stream.
RETURN VALUE
The
rewind()
function returns no value.
Upon successful completion,
fgetpos(),
fseek(),
fsetpos()
return 0,
and
ftell()
returns the current offset.
Otherwise, -1 is returned and
errno
is set to indicate the error.
ERRORS
- EINVAL
-
The
whence
argument to
fseek()
was not
SEEK_SET,
SEEK_END,
or
SEEK_CUR.
Or: the resulting file offset would be negative.
- ESPIPE
-
The file descriptor underlying
stream
is not seekable (e.g., it refers to a pipe, FIFO, or socket).
The functions
fgetpos(),
fseek(),
fsetpos(),
and
ftell()
may also fail and set
errno
for any of the errors specified for the routines
fflush(3),
fstat(2),
lseek(2),
and
malloc(3).
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
fseek(),
ftell(),
rewind(),
fgetpos(),
fsetpos()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, C89, C99.
SEE ALSO
lseek(2),
fseeko(3)
COLOPHON
This page is part of release 5.10 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.