问从Marshal.PtrToStringAnsi返回的字符串的编码是什么？

EN

{
    [ComVisible(true)]
    public class UTF8StringMarshaler : ICustomMarshaler
    {
        private static ICustomMarshaler marshalerInstance = new UTF8StringMarshaler();

        public static ICustomMarshaler GetInstance(string optionalCookie)
        {
            return marshalerInstance;
        }
        public void CleanUpManagedData(object ManagedObj)
        {
            //Managed Data will be deleted by the garbage collector
        }

        public void CleanUpNativeData(IntPtr pNativeData)
        {
            Marshal.FreeCoTaskMem(pNativeData);
        }

        public int GetNativeDataSize()
        {
            //Not used in our case
            return -1;
        }

        public IntPtr MarshalManagedToNative(object ManagedObj)
        {
            if (ManagedObj == null || ManagedObj as string == null)
                return IntPtr.Zero;

            if (!(ManagedObj is string))
                throw new MarshalDirectiveException("UTF8StringMarshaler can only be used on String.");

            UTF8Encoding utf8Encoder = new UTF8Encoding();
            string utf8string = ManagedObj as string;
            byte[] stringBuffer = utf8Encoder.GetBytes(utf8string);
            IntPtr buffer = Marshal.AllocCoTaskMem(stringBuffer.Length + 1);
            Marshal.Copy(stringBuffer, 0, buffer, stringBuffer.Length);
            Marshal.WriteByte(buffer + stringBuffer.Length, 0);
            return buffer;
        }

        public unsafe object MarshalNativeToManaged(IntPtr pNativeData)
        {
            if (pNativeData == IntPtr.Zero)
                return null;
            string temp = null;
            UTF8Encoding utf8Encoder = new UTF8Encoding(true, true);
            byte* buffer = (byte*)pNativeData;
            while (*buffer != 0)
            {
                buffer++;
            }
            int length = (int)(buffer - (byte*)pNativeData);

            byte[] stringbuffer = new byte[length];

            Marshal.Copy(pNativeData, stringbuffer, 0, length);
            try
            {
                temp = utf8Encoder.GetString(stringbuffer);
            }
            catch (EncoderFallbackException e)
            {
                Console.WriteLine("Encoding Exception type {0}, Error {1}", e.GetType().Name, e.Message);
            }
            return temp;
        }
    }