get nth occurance of a string by jaimthorn[at]yahoo[dot]com

/**
 *  Returns the position of the $nth occurrence of $needle in $haystack, or false if it doesn't exist, or false when illegal parameters have been supplied.
 *
 *  @param  string  $haystack   the string to search in.
 *  @param  string  $needle     the string to search for.
 *  @param  integer $nth        the number of the occurrence to look for.
 *  @param  integer $offset     the position in $haystack to start looking for $needle.
 *  @return MIXED   integer     either the position of the $nth occurrence of $needle in $haystack,
 *               or boolean     false if it can't be found.
 */
function strnpos( $haystack, $needle, $nth, $offset = 0 )
{
   if( 1 > $nth || 0 === strlen( $needle ) )
   {
       return false;
   }
 
   //  $offset is incremented in the call to strpos, so make sure that the first call starts at the right position by initially decrementing $offset.
   --$offset;
   do
   {
      $offset = strpos( $haystack, $needle, ++ $offset );
   } while( --$nth  && false !== $offset );
 
   return $offset;
}