/**
 * 生成随机字符串
* @param int       $length  要生成的随机字符串长度
* @param string    $type    随机码类型：0，数字+大小写字母；1，数字；2，小写字母；3，大写字母；4，特殊字符；-1，数字+大小写字母+特殊字符
* @return string
*/
function randCode($length = 12, $type = 0) {
    $arr = array(1 => "0123456789", 2 => "abcdefghijklmnopqrstuvwxyz", 3 => "ABCDEFGHIJKLMNOPQRSTUVWXYZ", 4 => "~@#$%^&*(){}[]|");
    if ($type == 0) {
      array_pop($arr);
      $string = implode("", $arr);
    } elseif ($type == "-1") {
        $string = implode("", $arr);
    } else {
      $string = $arr[$type];
    }
    
    $count = strlen($string) - 1;
    $code = '';
    for ($i = 0; $i < $length; $i++) {
      $code .= $string[rand(0, $count)];
    }
    return $code;
}