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 .