获取随机字符串

/**
 * 获取随机字符串
 * @param int $randLength 长度
 * @param int $addtime 是否加入时间戳
 * @param int $format 0:只字符 1:字符和数字 2:只数字
 * @return string
 */
function getRandStr($randLength=6, $addtime=1, $format=0){
    switch($format){
        case '0':
            $chars='abcdefghijklmnopqrstuvwxyz';
            break;
        case '1':
            $chars='abcdefghijklmnopqrstuvwxyzABCDEFGHJKLMNPQEST123456789';
            break;
        case '2':
            $chars='0123456789';
            break;
        default :
            $chars='abcdefghijklmnopqrstuvwxyzABCDEFGHJKLMNPQEST123456789';
            break;
    }
    $len=strlen($chars);
    $randStr='';
    for ($i=0;$i<$randLength;$i++){
        $randStr.=$chars[rand(0,$len-1)];
    }
    $tokenvalue=$randStr;
    if ($addtime){
        $tokenvalue=time().$randStr;
    }
    return $tokenvalue;
}