字符串生成

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//生成随机字符串
function  buildRandomString($type=1,$length=4){
    if($type==1){
        $chars=join('',range(0,9));
    }elseif($type==2){
        $chars=join('',array_merge(range('a','z'),array_merge('A','Z')));
    }elseif($type==3){
        $chars=join('',array_merge(range('a','z'),range('A','Z'),range(0,9)));
    }

    if($length>strlen($chars)){
        exit('字符串长度不够');
    }
    $chars=str_shuffle($chars);
    return substr($chars,0,$length);
}

//生成唯一字符串
function getUniName(){
    return md5(uniqid(microtime(true),true));
}
//得到文件扩展名
function getExt($filename){
    return strtolower(end(explode(".",$filename)));
}