PHP字符串倒叙

/**
 * 字符串转码 utf-8转换成gbk 或者gbk转换成utf-8
 * 
 * @param String $string 需要转码的字符串
 * @param String $toType 需要转换的字符编码，默认UTF-8
 *
 * @return String 返回转码后的字符串
 *
 */
function transCoding($string, $toType = "UTF-8")
{
    if ($toType == "UTF-8") {
        $string = iconv("GBK", "UTF-8", $string);
    } else {
        $string = iconv("UTF-8", "GBK", $string);
    }
    return $string;
}
$re = $this->transCoding('测试','GBK');
print_r($re);
$res = $this->transCoding($re,'UTF-8');
print_r($res);