(PHP 5 >= 5.3.0)
SplFixedArray::__construct — Constructs a new fixed array
$size = 0
  ] )
   Initializes a fixed array with a number of NULL values equal to size.
  
size
       The size of the fixed array. 
       This expects a number between 0 and PHP_INT_MAX.
      
No value is returned.
   Throws InvalidArgumentException when size is a negative
   number.
  
   Raises E_WARNING when size cannot be parsed as a number.
  
Example #1 SplFixedArray::__construct() example
<?php
$array = new SplFixedArray(5);
$array[1] = 2;
$array[4] = "foo";
foreach($array as $v) {
  var_dump($v);
}
?>
The above example will output:
NULL int(2) NULL NULL string(3) "foo"