how to generate random string in php

1. Mainly use two functions:

• chr()

• mt_rand()

2. Syntax format:

mt_rand() Use the Mersenne Twister algorithm to return a random integer.

mt_rand(min,max)

If the optional parameters min and max are not provided, mt_rand() Returns a pseudo-random number between 0 and RAND_MAX . For example, if you want a random number between 5 and 15 (inclusive), use mt_rand(5, 15). Many old libc random number generators have some uncertain and unknown characteristics and are very slow. PHP's rand() function uses the libc random number generator by default. mt_rand() The function is informally used to replace it. This function uses the known features in Mersenne Twister as a random number generator, which can generate random values ​​​​on average faster than rand() provided by libc Four times faster.

chr()Use an integer within the range of range (256) (that is, 0 to 255) as a parameter and return a corresponding character.

chr(i)

The return value is the ASCII character corresponding to the current integer.

3. Use the above two functions to generate a random string

<?php
  function getString($length = 4)
  {
    //从ASCII码中获取
    $captcha = &#39;&#39;;

    //随机取：大写、小写、数字
   for($i = 0;$i < $length; $i++){
     //随机确定是字母还是数字
     switch(mt_rand(1,3)){
         case 1:                //数字：49-57分别代表1-9
             $captcha .= chr(mt_rand(49,57));   
             break;
         case 2:                //小写字母:a-z
             $captcha .= chr(mt_rand(65,90));
             break;
         case 3:                //大写字母:A-Z
             $captcha .= chr(mt_rand(97,122));
             break;
      }
    }
    //返回
   return $captcha; 
   }
   
  echo getString(5);
?>

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