Trying to implement NTP Client using Managed C++ but getting date from 1899 using time.windows.com

Question

I am trying to implement a code to get time from time.windows.com but it returns a weird date (year of the date I get is 1899). Since the same servers work for my unmanaged C++ code using WinSock, I can imagine that something must be wrong with my code itself. Can someone look at my code below and tell me what I am doing wrong?

typedef unsigned int uint;
typedef unsigned long ulong;

long GetTimestampFromServer()
{
    System::String^ server = L"time.windows.com";

    array<unsigned char>^ ntpData = gcnew array<unsigned char>(48);
    ntpData[0] = 0x1B;

    array<System::Net::IPAddress^>^ addresses = System::Net::Dns::GetHostEntry(server)->AddressList;
    System::Net::IPEndPoint^ ipEndPoint = gcnew System::Net::IPEndPoint(addresses[0], 123);

    System::Net::Sockets::Socket^ socket = gcnew System::Net::Sockets::Socket
    (
        System::Net::Sockets::AddressFamily::InterNetwork,
        System::Net::Sockets::SocketType::Dgram,
        System::Net::Sockets::ProtocolType::Udp
    );

    try
    {
        socket->Connect(ipEndPoint);
        socket->ReceiveTimeout = 3000;
        socket->Send(ntpData);
        socket->Receive(ntpData);
        socket->Close();
    }
    catch (System::Exception^ e)
    {
        System::Console::WriteLine(e->Message);
        return 0;
    }

    const System::Byte serverReplyTime = 40;
    ulong intPart = System::BitConverter::ToUInt32(ntpData, serverReplyTime);
    ulong fractPart = System::BitConverter::ToUInt32(ntpData, serverReplyTime + 4);

    intPart = SwapEndianness(intPart);
    fractPart = SwapEndianness(fractPart);

    long long milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);

    System::DateTime networkDateTime = (gcnew System::DateTime(1900, 1, 1, 0, 0, 0, System::DateTimeKind::Utc))->AddMilliseconds((long)milliseconds);

    std::cout << ConvertToTimestamp(networkDateTime);

    return 0;
}

static uint SwapEndianness(ulong x)
{
    return (uint)(((x & 0x000000ff) << 24) +
        ((x & 0x0000ff00) << 8) +
        ((x & 0x00ff0000) >> 8) +
        ((x & 0xff000000) >> 24));
}

long ConvertToTimestamp(System::DateTime value)
{
    System::TimeZoneInfo^ NYTimeZone = System::TimeZoneInfo::FindSystemTimeZoneById(L"Eastern Standard Time");
    System::DateTime NyTime = System::TimeZoneInfo::ConvertTime(value, NYTimeZone);
    System::TimeZone^ localZone = System::TimeZone::CurrentTimeZone;
    System::Globalization::DaylightTime^ dst = localZone->GetDaylightChanges(NyTime.Year);
    NyTime = NyTime.AddHours(-1);
    System::DateTime epoch = System::DateTime(1970, 1, 1, 0, 0, 0, 0).ToLocalTime();
    System::TimeSpan span = (NyTime - epoch);
    return (long)System::Convert::ToDouble(span.TotalSeconds);
}

Answer 1

David Yaw pushed me in the right direction. Big thanks to him, I finally got my code to work. There was a lot of incorrectness associated with different statements throughout the method. I have fixed them and posting the new code below.

ref class SNTP
{
public: static DateTime GetNetworkTime()
{
    System::String^ ntpServer = "time.windows.com";

    auto ntpData = gcnew cli::array<unsigned char>(48);
    ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

    auto addresses = System::Net::Dns::GetHostEntry(ntpServer)->AddressList;
    auto ipEndPoint = gcnew System::Net::IPEndPoint(addresses[0], 123);

    auto socket = gcnew System::Net::Sockets::Socket
    (
        System::Net::Sockets::AddressFamily::InterNetwork,
        System::Net::Sockets::SocketType::Dgram,
        System::Net::Sockets::ProtocolType::Udp
    );

    socket->Connect(ipEndPoint);
    socket->ReceiveTimeout = 3000;
    socket->Send(ntpData);
    socket->Receive(ntpData);
    socket->Close();

    const System::Byte serverReplyTime = 40;

    System::UInt64 intPart = System::BitConverter::ToUInt32(ntpData, serverReplyTime);
    System::UInt64 fractPart = System::BitConverter::ToUInt32(ntpData, serverReplyTime + 4);

    intPart = SwapEndianness(intPart);
    fractPart = SwapEndianness(fractPart);

    auto milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);

    auto networkDateTime = (System::DateTime(1900, 1, 1, 0, 0, 0, System::DateTimeKind::Utc)).AddMilliseconds((System::Int64)milliseconds);

    return networkDateTime.ToLocalTime();
}
private: static System::UInt32 SwapEndianness(System::UInt64 x)
{
    return (System::UInt32)(((x & 0x000000ff) << 24) +
        ((x & 0x0000ff00) << 8) +
        ((x & 0x00ff0000) >> 8) +
        ((x & 0xff000000) >> 24));
}
};