PHP函数strtotime的扩展

    function add_month ( $base_time = null, $months = 1 )
    {
        if ( is_null ( $base_time ) )
            $base_time = time();

        $x_months_to_the_future = strtotime ( "+" . $months . " months", $base_time );

        $month_before = ( int ) date ( "m", $base_time ) + 12 * ( int ) date ( "Y", $base_time );
        $month_after = ( int ) date ( "m", $x_months_to_the_future ) + 12 * ( int ) 
        date ( "Y", $x_months_to_the_future );

        if ( $month_after > $months + $month_before )
        {
            $x_months_to_the_future = strtotime ( date ( "Ym01His", $x_months_to_the_future ) . " -1 day" );
        }
        return $x_months_to_the_future;
    }