安全注意:在随机性质量可能影响应用程序安全性的情况下，不应使用此解决方案。特别是，rand()和uniqid()不是加密安全的随机数生成器。关于安全的替代方案，请参阅Scott的回答。

如果你不需要它随着时间的推移是绝对唯一的:

md5 (uniqid (rand()、true))

否则(假设你已经为你的用户确定了一个唯一的登录):

md5(uniqid($your_user_login, true))

我们可以使用这个代码。我测试了35000个id，没有重复。

<?php
$characters = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_';
$result = '';
for ($i = 0; $i < 11; $i++)
    $result .= $characters[mt_rand(0, 63)];?>

您可以根据需要自由修改它。如果你有任何建议，请随意评论。建议您在使用这些id之前检查数据库中的每个id，这样您的数据库中就有100%唯一的id。

生成一个随机数使用 你最喜欢的随机数 发电机 乘除 得到一个与数字匹配的数字 你的代码字母表中的字符 将该索引处的项插入 你的代码字母。 重复1)，直到你有你想要的长度 想要

例如(伪代码)

int myInt = random(0, numcharacters)
char[] codealphabet = 'ABCDEF12345'
char random = codealphabet[i]
repeat until long enough

对于真正随机的字符串，你可以用

<?php

echo md5(microtime(true).mt_Rand());

输出:

40a29479ec808ad4bcff288a48a25d5c

因此，即使您尝试在同一时间多次生成字符串，也会得到不同的输出。

我用了这样一句话:

base64_encode(openssl_random_pseudo_bytes(3 * ($length >> 2)));

其中length是所需字符串的长度(能被4整除，否则它会四舍五入到最接近的能被4整除的数字)

一个简单的解决方案是通过丢弃非字母数字字符将64进制转换为字母数字。

它使用random_bytes()来获得加密安全的结果。

function random_alphanumeric(int $length): string
{
    $result='';
    do
    {
        //Base 64 produces 4 characters for each 3 bytes, so most times this will give enough bytes in a single pass
        $bytes=random_bytes(($length+3-strlen($result))*2);
        //Discard non-alhpanumeric characters
        $result.=str_replace(['/','+','='],['','',''],base64_encode($bytes));
        //Keep adding characters until the string is long enough
        //Add a few extra because the last 2 or 3 characters of a base 64 string tend to be less diverse
    }while(strlen($result)<$length+3);
    return substr($result,0,$length);
}

编辑:我只是重新审视了一下，因为我需要一些更灵活的东西。这里有一个解决方案，执行得比上面的好一点，并提供了指定ASCII字符集的任何子集的选项:

<?php
class RandomText
{
    protected
        $allowedChars,
        //Maximum index to use
        $allowedCount,
        //Index values will be taken from a pool of this size
        //It is a power of 2 to keep the distribution of values even
        $distributionSize,
        //This many characters will be generated for each output character
        $ratio;
    /**
     * @param string $allowedChars characters to choose from
     */
    public function __construct(string $allowedChars)
    {
        $this->allowedCount = strlen($allowedChars);
        if($this->allowedCount < 1 || $this->allowedCount > 256) throw new \Exception('At least 1 and no more than 256 allowed character(s) must be specified.');
        $this->allowedChars = $allowedChars;
        //Find the power of 2 equal or greater than the number of allowed characters
        $this->distributionSize = pow(2,ceil(log($this->allowedCount, 2)));
        //Generating random bytes is the expensive part of this algorithm
        //In most cases some will be wasted so it is helpful to produce some extras, but not too many
        //On average, this is how many characters needed to produce 1 character in the allowed set
        //50% of the time, more characters will be needed. My tests have shown this to perform well.
        $this->ratio = $this->distributionSize / $this->allowedCount;
    }

    /**
     * @param int $length string length of required result
     * @return string random text
     */
    public function get(int $length) : string
    {
        if($length < 1) throw new \Exception('$length must be >= 1.');
        $result = '';
        //Keep track of result length to prevent having to compute strlen()
        $l = 0;
        $indices = null;
        $i = null;
        do
        {
            //Bytes will be used to index the character set. Convert to integers.
            $indices = unpack('C*', random_bytes(ceil(($length - $l) * $this->ratio)));
            foreach($indices as $i)
            {
                //Reduce to the smallest range that gives an even distribution
                $i %= $this->distributionSize;
                //If the index is within the range of characters, add one char to the string
                if($i < $this->allowedCount)
                {
                    $l++;
                    $result .= $this->allowedChars[$i];
                }
                if($l >= $length) break;
            }
        }while($l < $length);
        return $result;
    }
}