Detailed explanation of the steps to generate a random string of custom length in PHP

This time I will bring you a detailed explanation of the steps to generate a random string with a custom length in php. What are the precautions for generating a random string with a custom length in php? The following is a practical case. , let’s take a look.

//随机生成字符串
function random($length) {
     srand(date("s"));
     $possible_charactors = "0123456789abcdefghijklmnopqrstuvwxyz";
     $string = "";
     while(strlen($string)<$length) {
          $string .= substr($possible_charactors,(rand()%(strlen($possible_charactors))),1);
     }
     return($string);
}

Use php to generate n non-repeating random number instances

A programmer made a mistake earlier and forgot to store the votes in the database. The voting sequences generated by 200 users were empty. So how do you fill this gap?
Need to generate 16 non-repeating random numbers between 1-25 to fill. How to design the function specifically? Store random numbers in an array, and then remove duplicate values ​​in the array to generate a certain number of non-repeating random numbers.
Program:

<?php
/*
* array unique_rand( int $min, int $max, int $num )
* 生成一定数量的不重复随机数
* $min 和 $max: 指定随机数的范围
* $num: 指定生成数量
*/ www.jbxue.com
function unique_rand($min, $max, $num) {
    $count = 0;
    $return = array();
    while ($count < $num) {
        $return[] = mt_rand($min, $max);
        $return = array_flip(array_flip($return));
        $count = count($return);
    }
    shuffle($return);
    return $return;
}
$arr = unique_rand(1, 25, 16);
sort($arr);
$result = &#39;&#39;;
for($i=0; $i < count($arr);$i++)
{
 $result .= $arr[$i].&#39;,&#39;;
}
$result = substr($result, 0, -1);
echo $result;
?>

2,3,4,6,7,8,9,10,11,12,13,16,20,21,22,24

The mt_rand() function is used to generate random numbers. This function generates random numbers four times faster on average than rand().
The "flip method" is used to remove duplicate values ​​in the array, which is to use array_flip() to exchange the key and value of the array twice. This approach is much faster than using
array_unique(). Before returning the array, first use shuffle() to assign new key names to the array, ensuring that the key names are consecutive numbers from 0-n. If this step is not performed, the key names may be discontinuous when
deleting duplicate values, causing trouble for traversal.

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