FSEEK(3P)                                           POSIX Programmer's Manual                                          FSEEK(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

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-posi-
       tion 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  out-
       put.

       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 unwrit-
       ten 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 condi-
              tions.

       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, Copy-
       right (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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                     FSEEK(3P)