C#处理乱码问题

extern "C" __declspec(dllexport) int scanRe(char* data)
{
    strcpy(data,"47");
    return 0;
}
在c#中接收返回值用 ref byte
        [DllImport("PDAScandll.dll",CharSet=System.Runtime.InteropServices.CharSet.Auto)]
        public static extern int scanRe( ref byte param2);
        private void button1_Click(object sender, EventArgs e)
        {
            byte[] param2 = new byte[255];//新建字节数组
           
            scanRe(ref param2[0]);//向dll函数传入参数

            string s = System.Text.Encoding.GetEncoding("GB2312").GetString(param2, 0, param2.Length);
            //将字节数组转换为字符串

            label1.Text =s;
          ｝