.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "FSEEK" 3P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" fseek 
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.SH NAME
fseek, fseeko \- reposition a file-position indicator in a stream
.SH SYNOPSIS
.LP
\fB#include <stdio.h>
.br
.sp
int fseek(FILE *\fP\fIstream\fP\fB, long\fP \fIoffset\fP\fB, int\fP
\fIwhence\fP\fB);
.br
\fP
.LP
\fBint fseeko(FILE *\fP\fIstream\fP\fB, off_t\fP \fIoffset\fP\fB,
int\fP \fIwhence\fP\fB);
\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIfseek\fP() function shall set the file-position indicator for
the stream pointed to by \fIstream\fP. If a read or write
error occurs, the error indicator for the stream shall be set and
\fIfseek\fP() fails.
.LP
The new position, measured in bytes from the beginning of the file,
shall be obtained by adding \fIoffset\fP to the position
specified by \fIwhence\fP. The specified point is the beginning of
the file for SEEK_SET, the current value of the file-position
indicator for SEEK_CUR, or end-of-file for SEEK_END.
.LP
If the stream is to be used with wide-character input/output functions,
the application shall ensure that \fIoffset\fP is
either 0 or a value returned by an earlier call to \fIftell\fP() on
the same stream and
\fIwhence\fP is SEEK_SET.
.LP
A successful call to \fIfseek\fP() shall clear the end-of-file indicator
for the stream and undo any effects of \fIungetc\fP() and \fIungetwc\fP()
on the same stream.
After an \fIfseek\fP() call, the next operation on an update stream
may be either input or output.
.LP
If
the most recent operation, other than \fIftell\fP(), on a given stream
is \fIfflush\fP(), the file offset in the underlying open file description
shall be adjusted to
reflect the location specified by \fIfseek\fP().
.LP
The \fIfseek\fP() function shall allow the file-position indicator
to be set beyond the end of existing data in the file. If
data is later written at this point, subsequent reads of data in the
gap shall return bytes with the value 0 until data is actually
written into the gap.
.LP
The behavior of \fIfseek\fP() on devices which are incapable of seeking
is implementation-defined. The value of the file offset
associated with such a device is undefined.
.LP
If the stream is writable and buffered data had not been written to
the underlying file, \fIfseek\fP() shall cause the
unwritten data to be written to the file and shall mark the \fIst_ctime\fP
and \fIst_mtime\fP fields of the file for update.
.LP
In a locale with state-dependent encoding, whether \fIfseek\fP() restores
the stream's shift state is
implementation-defined.
.LP
The \fIfseeko\fP() function shall be equivalent to the \fIfseek\fP()
function except that the \fIoffset\fP argument is of
type \fBoff_t\fP. 
.SH RETURN VALUE
.LP
The \fIfseek\fP()  and \fIfseeko\fP()  functions
shall return 0 if they succeed.
.LP
Otherwise, they shall return -1 and set \fIerrno\fP to indicate the
error. 
.SH ERRORS
.LP
The \fIfseek\fP()  and \fIfseeko\fP() 
\ functions shall fail if,  either the \fIstream\fP is unbuffered
or the \fIstream\fP's buffer needed to be flushed, and
the call to \fIfseek\fP() or \fIfseeko\fP() causes an underlying \fIlseek\fP()
or \fIwrite\fP() to be invoked, and: 
.TP 7
.B EAGAIN
The O_NONBLOCK flag is set for the file descriptor and the process
would be delayed in the write operation. 
.TP 7
.B EBADF
The file descriptor underlying the stream file is not open for writing
or the stream's buffer needed to be flushed and the file is
not open. 
.TP 7
.B EFBIG
An
attempt was made to write a file that exceeds the maximum file size.
.TP 7
.B EFBIG
An attempt was made to write a file that exceeds the process' file
size limit. 
.TP 7
.B EFBIG
The file is a regular file and an attempt was made to write at or
beyond the offset maximum associated with the corresponding
stream. 
.TP 7
.B EINTR
The write operation was terminated due to the receipt of a signal,
and no data was transferred. 
.TP 7
.B EINVAL
The \fIwhence\fP argument is invalid. The resulting file-position
indicator would be set to a negative value. 
.TP 7
.B EIO
A
physical I/O error has occurred, or the process is a member of a background
process group attempting to perform a \fIwrite\fP() to its controlling
terminal, TOSTOP is set, the process is neither ignoring nor
blocking SIGTTOU, and the process group of the process is orphaned.
This error may also be returned under implementation-defined
conditions. 
.TP 7
.B ENOSPC
There was no free space remaining on the device containing the file.
.TP 7
.B ENXIO
A
request was made of a nonexistent device, or the request was outside
the capabilities of the device. 
.TP 7
.B EOVERFLOW
For \fIfseek\fP(), the resulting file offset would be a value which
cannot be represented correctly in an object of type
\fBlong\fP. 
.TP 7
.B EOVERFLOW
For \fIfseeko\fP(), the resulting file offset would be a value which
cannot be represented correctly in an object of type
\fBoff_t\fP. 
.TP 7
.B EPIPE
An
attempt was made to write to a pipe or FIFO that is not open for reading
by any process; a SIGPIPE signal shall also be sent to the
thread. 
.TP 7
.B ESPIPE
The file descriptor underlying \fIstream\fP is associated with a pipe
or FIFO. 
.sp
.LP
\fIThe following sections are informative.\fP
.SH EXAMPLES
.LP
None.
.SH APPLICATION USAGE
.LP
None.
.SH RATIONALE
.LP
None.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIfopen\fP(), \fIfsetpos\fP(), \fIftell\fP(),
\fIgetrlimit\fP(), \fIlseek\fP(), \fIrewind\fP(), \fIulimit\fP(),
\fIungetc\fP(), \fIwrite\fP(), the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, \fI<stdio.h>\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .