为什么 PHP 选择这样的随机值？

Question

所以...我正在测试一些东西并注意到当我运行这段代码时：

$arr = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890", 1);
print_r(implode(array_rand(array_flip($arr), 16)));

输出是

Refresh 1: BDFIJKPTVkl12789
Refresh 2: HIJKMQWYdfmorsw3
Refresh 3: FGHMNRVYfhknouw5
Refresh 4: AFIJKRSVeiuwx579
Refresh 5: DJORYZcgijlpqry1
Refresh 6: EISWbhjmoqr45689
Refresh 7: CDEFOTXdhkloqr27
Refresh 8: AEFIKLNORSknx349
Refresh 9: DEFHJMTVZcgpstz0
Refresh 10: CLQTZbefhnpq1279

Why does the output start everytime with 1 to 5 uppercase letters? That "randomness" seems weird to me.

我想知道为什么会得到这个结果。

Answer 1

array_rand (since PHP 5.2.10) no longer shuffles the list of random keys that it generates (you'll notice that your output strings are all in alphabetical order i.e. the characters are in the same order as they are in the input string). If you don't want that behaviour, use shuffle and array_slice 改为：

$arr = str_split("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890", 1);
shuffle($arr);
echo implode('', array_slice($arr, 0, 16));

输出：

dU54f9wBjZbAKgCP

Demo on 3v4l.org

为什么 PHP 选择这样的随机值？

Why is PHP selecting the Random Values like that?

php

arrays

random

undefined-behavior