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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 dif-
       fer (consult 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-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  off-
       set 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 under-
       lying 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 opera-
              tion.

       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, Stan-
       dard  for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifica-
       tions 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 Stan-
       dard, 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 .



IEEE/The Open Group                  2003                            FSEEK(3P)