字符串中的数组语法:未初始化的字符串偏移错误 [英] Array syntax in string: Uninitialized string offset error

问题描述

我在以下在线发布的代码中得到了一个未初始化的字符串偏移量:

I'm getting an unitialized string offset in the following code that was posted online:

function generateKey() {
    $length = 15;
    $characters = '0123456789abcdefghijklmnopqrstuvwxyz';
    $string = '';
    for ($p = 0; $p < $length; $p++) {
        $string .= $characters[mt_rand(0, strlen($characters))];
    }
    return $string;
}

是不是因为 $characters[] 被应用于字符串?我不完全明白错误意味着什么，但我如何才能达到同样的效果并解决这个问题(它现在工作正常，只是抛出一个错误)?

Is it because of $characters[] being applied to a string? I don't fully get what the error means, but how could I achieve the same effect and get around that (it's working fine right now, just throwing an error)?

推荐答案

基本上已经回答了，但我建议

Basically what has been already answered, but I suggest

• 只执行一次 strlen() 操作并将最大随机数存储到一个变量中，
• 初始化 $string 缓冲区并写入其中，而不是进行连续的连接，
• 减少计数器 $p 以便从后到前工作.

• do the strlen() operation only once and store the maximum random number into a variable,
• initialize the $string buffer and write into it instead of an ongoing concatenation,
• decrease the counter $p so to work from back to front.

演示，代码:

function generateKey() {
    $length = 15;
    $characters = '0123456789abcdefghijklmnopqrstuvwxyz';
    $maxrnd = strlen($characters)-1;
    $string = str_repeat('0', $length);
    for ($p = $length; $p--;) {
        $string[$p] = $characters[mt_rand(0, $maxrnd)];
    }
    return $string;
}

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