PHP获取随机字符串的两种方法

 <?php
 /**
  * 随机返回字符串
  * @param number 返回字符串长度
  * @param string 从哪些字符串中随机返回，已设置默认字符串，可空
  * @return string 返回随机字符串
  */
 function random_string($length = 8, $chars = null) {
     static $s;
     if( empty($chars) ) $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
     while( strlen($s) < $length) {
         $s .= substr($chars, rand(0, strlen($chars) - 1), 1);
     }
     return $s;
 }

 function random_string2($length = 8, $chars_range = 'alpha-number') {
     $str = '';
     $chars = '';
     $char_arr = array(
             "alpha" => "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz",
             "number" => "0123456789",
     );
     if (empty($chars_range)) {
         $chars_rang = 'alpha-number';
     }
     if(strpos($chars_range, '-')) {
         $char_range_arr = explode('-',$chars_range);
         foreach($char_range_arr as $range){
             if(!array_key_exists($range, $char_arr)){
                 exit("wrong range \"". $range ."\"");
             }
             $chars .= $char_arr[$range];
         }
     }else{
         if(!array_key_exists($chars_range, $char_arr)){
             exit("wrong range \"".$chars_range ."\"");
         }
         $chars = $char_arr[$chars_range];
     }
     while( strlen($str) < $length) {
         $str .= substr($chars, rand(0, strlen($chars) - 1), 1);
     }
     return $str;
 }

 ?>