php函数获取当月多少天

    $days = cal_days_in_month(CAL_GREGORIAN, 4, 2011);
    echo "返回2011-4的天数 ".$days."<br/>";
    $days = date('t', strtotime("2011-4-1"));
    echo "返回2011-4的天数 ".$days."<br/>";
    $days = date("t"); 
    echo "当前月的天数 ".$days."<br/>";

利用 cal_days_in_month(CAL_GREGORIAN,月,年)函数