(PHP 5)
vfprintf — Write a formatted string to a stream
$handle
   , string $format
   , array $args
   )
   Write a string produced according to format to the
   stream resource specified by handle.
  
Operates as fprintf() but accepts an array of arguments, rather than a variable number of arguments.
Returns the length of the outputted string.
Example #1 vfprintf(): zero-padded integers
<?php
if (!($fp = fopen('date.txt', 'w')))
    return;
vfprintf($fp, "%04d-%02d-%02d", array($year, $month, $day));
// will write the formatted ISO date to date.txt
?>