日期差 php时间比较函数，返回两个日期相差几秒、几分钟、几小时或几天

function DateDiff($date1, $date2, $unit = "") { //时间比较函数，返回两个日期相差几秒、几分钟、几小时或几天 
    switch ($unit) { 
        case 's': 
            $dividend = 1; 
            break; 
        case 'i': 
            $dividend = 60; //oSPHP.COM.CN 
            break; 
        case 'h': 
            $dividend = 3600; 
            break; 
        case 'd': 
            $dividend = 86400; 
            break; //开源OSPhP.COM.CN 
        default: 
            $dividend = 86400; 
    } 
    $time1 = strtotime($date1); 
    $time2 = strtotime($date2); 
    if ($time1 && $time2) 
        return (float)($time1 - $time2) / $dividend; 
    return false; 
}