php 随机生成字符串的函数

  /**  * php 生成随机字符  * @param number $length 长度  * @param string $type 类型  * @param number $convert 转换大小写  * @return string  */  function random($length=6, $type='string', $convert=0){      $config = array(          'number'=>'1234567890',          'letter'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ',          'string'=>'abcdefghjkmnpqrstuvwxyzABCDEFGHJKMNPQRSTUVWXYZ23456789',          'all'=>'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890'      );            if(!isset($config[$type])) $type = 'string';      $string = $config[$type];            $code = '';      $strlen = strlen($string) -1;      for($i = 0; $i < $length; $i++){          $code .= $string{mt_rand(0, $strlen)};      }      if(!empty($convert)){          $code = ($convert > 0)? strtoupper($code) : strtolower($code);      }      return $code;  }