PHP獲取隨機字符串的兩種方法

<?php
/**
 * 隨機返回字符串
 * @param number 返回字符串長度
 * @param string 從哪些字符串中隨機返回，已設置默認字符串，可空
 * @return string 返回隨機字符串
 */
function random_string($length = 8, $chars = null) {
    static $s;
    if( empty($chars) ) $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
    while( strlen($s) < $length) {
        $s .= substr($chars, rand(0, strlen($chars) - 1), 1);
    }
    return $s;
}

function random_string2($length = 8, $chars_range = 'alpha-number') {
    $str = '';
    $chars = '';
    $char_arr = array(
            "alpha" => "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz",
            "number" => "0123456789",
    );
    if (empty($chars_range)) {
        $chars_rang = 'alpha-number';
    }
    if(strpos($chars_range, '-')) {
        $char_range_arr = explode('-',$chars_range);
        foreach($char_range_arr as $range){
            if(!array_key_exists($range, $char_arr)){
                exit("wrong range \"". $range ."\"");
            }
            $chars .= $char_arr[$range];
        }
    }else{
        if(!array_key_exists($chars_range, $char_arr)){
            exit("wrong range \"".$chars_range ."\"");
        }
        $chars = $char_arr[$chars_range];
    }
    while( strlen($str) < $length) {
        $str .= substr($chars, rand(0, strlen($chars) - 1), 1);
    }
    return $str;
}

?>