<?
   $string = "a          b c d e f";

   $tok = strtok($string, " ");

   while($tok) {
      printf("[%s]\n", $tok);
      $tok = strtok(" ");
   }

?>

 result is

 [a]

 if string is "a b c d e f", then result is correct, but
    string "a  b  c  d  e  f"  is not work.