php - 生成随机GUID时未初始化的字符串偏移量通知

Question

我有一个导致上述错误反复出现在我的错误日志中的代码，我该如何纠正它？

public function generate_guid() {
        //you can change the length of the autogenerated guid here
        //i choose 4 because with 26 possible characters that still gives 456.976 possibilities, if you include numbers ( add 0123456789) to the possible characters you will get 1.679.616 combinations
        $length = 4;
         //charachters used for string generation
    $characters = 'abcdefghijklmnopqrstuvwxyz';
    $string = '';    
    for ($p = 0; $p < $length; $p++) {
    $string .= $characters[mt_rand(0, strlen($characters))]; <<-- this is line 92
}
return $string;
    }

Answer 1

问题是mt_rand(0, strlen($characters))会生成直至字符串长度的数字-但是当字符串偏移量从0开始时，最大偏移量就是长度减去一。因此正确的是mt_rand(0, strlen($characters) - 1)。

顺便说一句，我建议使用range('a', 'z')生成的字符数组(这样就不必键入它)，并建议使用array_rand获取元素。