<?php
/**
 *生成随机数，可用户验证码
 *@param
 */
function randStr($m = 5) {
 $new_str = '';
 $str = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwsyz0123456789';
 $max=strlen($str)-1;
 for ($i = 1; $i <= $m; ++$i) {
  $new_str .=$str[mt_rand(0, $max)];
 }
 return $new_str;
}
//测试
$str = randStr(6);
echo $str;