FSEEK
Section: POSIX Programmer's Manual (P)
Updated: 2003
NAME
fseek, fseeko - reposition a file-position indicator in a stream
SYNOPSIS
#include <stdio.h>
int fseek(FILE *stream, long offset, int
whence);
int fseeko(FILE *stream, off_t offset,
int whence);
DESCRIPTION
The fseek() function shall set the file-position indicator for
the stream pointed to by stream. If a read or write
error occurs, the error indicator for the stream shall be set and
fseek() fails.
The new position, measured in bytes from the beginning of the file,
shall be obtained by adding offset to the position
specified by whence. 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.
If the stream is to be used with wide-character input/output functions,
the application shall ensure that offset is
either 0 or a value returned by an earlier call to ftell() on
the same stream and
whence is SEEK_SET.
A successful call to fseek() shall clear the end-of-file indicator
for the stream and undo any effects of ungetc() and ungetwc()
on the same stream.
After an fseek() call, the next operation on an update stream
may be either input or output.
If
the most recent operation, other than ftell(), on a given stream
is fflush(), the file offset in the underlying open file description
shall be adjusted to
reflect the location specified by fseek().
The fseek() 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.
The behavior of fseek() on devices which are incapable of seeking
is implementation-defined. The value of the file offset
associated with such a device is undefined.
If the stream is writable and buffered data had not been written to
the underlying file, fseek() shall cause the
unwritten data to be written to the file and shall mark the st_ctime
and st_mtime fields of the file for update.
In a locale with state-dependent encoding, whether fseek() restores
the stream's shift state is
implementation-defined.
The fseeko() function shall be equivalent to the fseek()
function except that the offset argument is of
type off_t.
RETURN VALUE
The fseek() and fseeko() functions
shall return 0 if they succeed.
Otherwise, they shall return -1 and set errno to indicate the
error.
ERRORS
The fseek() and fseeko()
functions shall fail if, either the stream is unbuffered
or the stream's buffer needed to be flushed, and
the call to fseek() or fseeko() causes an underlying lseek()
or write() to be invoked, and:
- EAGAIN
-
The O_NONBLOCK flag is set for the file descriptor and the process
would be delayed in the write operation.
- 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.
- EFBIG
-
An
attempt was made to write a file that exceeds the maximum file size.
- EFBIG
-
An attempt was made to write a file that exceeds the process' file
size limit.
- 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.
- EINTR
-
The write operation was terminated due to the receipt of a signal,
and no data was transferred.
- EINVAL
-
The whence argument is invalid. The resulting file-position
indicator would be set to a negative value.
- EIO
-
A
physical I/O error has occurred, or the process is a member of a background
process group attempting to perform a write() 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.
- ENOSPC
-
There was no free space remaining on the device containing the file.
- ENXIO
-
A
request was made of a nonexistent device, or the request was outside
the capabilities of the device.
- EOVERFLOW
-
For fseek(), the resulting file offset would be a value which
cannot be represented correctly in an object of type
long.
- EOVERFLOW
-
For fseeko(), the resulting file offset would be a value which
cannot be represented correctly in an object of type
off_t.
- 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.
- ESPIPE
-
The file descriptor underlying stream is associated with a pipe
or FIFO.
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
None.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
fopen() , fsetpos() , ftell()
, getrlimit() , lseek() , rewind() , ulimit()
, ungetc() , write() , the Base Definitions volume of
IEEE Std 1003.1-2001, <stdio.h>
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 .
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- EXAMPLES
-
- APPLICATION USAGE
-
- RATIONALE
-
- FUTURE DIRECTIONS
-
- SEE ALSO
-
- COPYRIGHT
-
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