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.\" on Information Processing Systems.

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.\"     @(#)fseek.3	6.11 (Berkeley) 6/29/91

.\"

.\" Converted for Linux, Mon Nov 29 15:22:01 1993, faith@cs.unc.edu

.\"

.TH FSEEK 3  2017-09-15 "GNU" "Linux Programmer's Manual"

.SH NAME

fgetpos, fseek, fsetpos, ftell, rewind \- reposition a stream

.SH SYNOPSIS

.B #include <stdio.h>

.PP

.BI "int fseek(FILE *" stream ", long " offset ", int " whence );

.PP

.BI "long ftell(FILE *" stream );

.PP

.BI "void rewind(FILE *" stream );

.PP

.BI "int fgetpos(FILE *" stream ", fpos_t *" pos );

.PP

.BI "int fsetpos(FILE *" stream ", const fpos_t *" pos );

.SH DESCRIPTION

The

.BR fseek ()

function sets the file position indicator for the stream pointed to by

.IR stream .

The new position, measured in bytes, is obtained by adding

.I offset

bytes to the position specified by

.IR whence .

If

.I whence

is set to

.BR SEEK_SET ,

.BR SEEK_CUR ,

or

.BR 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

.BR fseek ()

function clears the end-of-file indicator for the stream and undoes

any effects of the

.BR ungetc (3)

function on the same stream.

.PP

The

.BR ftell ()

function obtains the current value of the file position indicator for the

stream pointed to by

.IR stream .

.PP

The

.BR rewind ()

function sets the file position indicator for the stream pointed to by

.I stream

to the beginning of the file.

It is equivalent to:

.PP

.RS

(void) fseek(stream, 0L, SEEK_SET)

.RE

.PP

except that the error indicator for the stream is also cleared (see

.BR clearerr (3)).

.PP

The

.BR fgetpos ()

and

.BR fsetpos ()

functions are alternate interfaces equivalent to

.BR ftell ()

and

.BR fseek ()

(with

.I whence

set to

.BR SEEK_SET ),

setting and storing the current value of the file offset into or from the

object referenced by

.IR pos .

On some non-UNIX systems, an

.I fpos_t

object may be a complex object and these routines may be the only way to

portably reposition a text stream.

.SH RETURN VALUE

The

.BR rewind ()

function returns no value.

Upon successful completion,

.BR fgetpos (),

.BR fseek (),

.BR fsetpos ()

return 0,

and

.BR ftell ()

returns the current offset.

Otherwise, \-1 is returned and

.I errno

is set to indicate the error.

.SH ERRORS

.TP

.B EBADF

The

.I stream

specified is not a seekable stream.

.TP

.B EINVAL

The

.I whence

argument to

.BR fseek ()

was not

.BR SEEK_SET ,

.BR SEEK_END ,

or

.BR SEEK_CUR .

Or: the resulting file offset would be negative.

.PP

The functions

.BR fgetpos (),

.BR fseek (),

.BR fsetpos (),

and

.BR ftell ()

may also fail and set

.I errno

for any of the errors specified for the routines

.BR fflush (3),

.BR fstat (2),

.BR lseek (2),

and

.BR malloc (3).

.SH ATTRIBUTES

For an explanation of the terms used in this section, see

.BR attributes (7).

.TS

allbox;

lbw27 lb lb

l l l.

Interface	Attribute	Value

T{

.BR fseek (),

.BR ftell (),

.BR rewind (),

.br

.BR fgetpos (),

.BR fsetpos ()

T}	Thread safety	MT-Safe

.TE

.sp 1

.SH CONFORMING TO

POSIX.1-2001, POSIX.1-2008, C89, C99.

.SH SEE ALSO

.BR lseek (2),

.BR fseeko (3)

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I 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/.