PHP to get four-digit letters and numbers of random number implementation method _php tips

So we know that simple four-digit pure digital verification in PHP can be done with Rand (1000,9999), but if we're going to get a random four-digit number of letters and numbers, how do we write a function? The following Hu Peng blog in the PHP data column gives a complete example.

<?php
function Getfourstr ($len) 
{ 
  $chars _array = Array ( 
    "0", "1", "2", "3", "4", "5", "6", "7", "8", "9 ","
    a "," B "," C "," D "," E "," F "," G "," H "," I "," J "," K "," 
    L "," M "," N "," O "," P "," Q "," R "," s "," T "," U "," V ", 
   "W", "X", "Y", "Z", "A", "B", "C", "D", "E", "F", "G", " 
    H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", 
    " S "," T "," U "," V "," W "," X "," Y "," Z ", 
  ); 
  $charsLen = count ($chars _array)-1; 
 
  $outputstr = ""; 
  for ($i =0; $i < $len; $i + +) 
  { 
    $outputstr. = $chars _array[mt_rand (0, $charsLen)]; 
  } 
  return $outputstr; 
} 
Echo Getfourstr (4);
? >

Part of the function parsing: mt_rand function Description: Mt_rand () returns a random integer.
If the optional parameter min and Max,mt_rand () are not provided, the pseudo random number between 0 and Rand_max is returned. For example, want a random number between 0 and 46 (including 0 and 46), with Mt_rand (0, 46).