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 .