php man page for fseek

FSEEK(3)								 1								  FSEEK(3)

fseek - Seeks on a file pointer

SYNOPSIS
       int fseek (resource  $handle, int  $offset, [int  $whence = SEEK_SET])

DESCRIPTION
	Sets  the  file position indicator for the file referenced by $handle. The new position, measured in bytes from the beginning of the file,
       is obtained by adding $offset to the position specified by $whence.

	In general, it is allowed to seek past the end-of-file; if data is then written, reads in any unwritten region between the end-of-file and
       the  sought  position  will  yield bytes with value 0. However, certain streams may not support this behavior, especially when they have an
       underlying fixed size storage.

PARAMETERS
	      o $handle
		-A file system pointer resource that is typically created using fopen(3).

	      o $offset
		- The offset.  To move to a position before the end-of-file, you need to pass a negative value	in  $offset  and  set  $whence	to
		SEEK_END.

	      o $whence
		-$whence values are:

		     o SEEK_SET - Set position equal to $offset bytes.

		     o SEEK_CUR - Set position to current location plus $offset.

		     o SEEK_END - Set position to end-of-file plus $offset.

RETURN VALUES
	Upon success, returns 0; otherwise, returns -1.

EXAMPLES
       Example #1

	      fseek(3) example

	      <?php

	      $fp = fopen('somefile.txt', 'r');

	      // read some data
	      $data = fgets($fp, 4096);

	      // move back to the beginning of the file
	      // same as rewind($fp);
	      fseek($fp, 0);

	      ?>

NOTES
       Note

	       If  you	have  opened the file in append ( a or a+) mode, any data you write to the file will always be appended, regardless of the
	      file position, and the result of calling fseek(3) will be undefined.

       Note

	       Not all streams support seeking. For those that do not support seeking, forward seeking from the current position  is  accomplished
	      by reading and discarding data; other forms of seeking will fail.

SEE ALSO
       ftell(3), rewind(3).

PHP Documentation Group 														  FSEEK(3)