Questions of using UdpClient.BeginReceive Method in VC++

  • Thread starter Thread starter tccode97
  • Start date Start date
T

tccode97

To whom it may concern,

I am developing a socket application in VC++ that uses asynchronous
connnection.

After doing search on google, I found the following link

http://msdn2.microsoft.com/en-us/library/system.net.sockets.udpclient.beginreceive.aspx

First of all, thanks for microsoft team for this post.

However I have couple questions concerning the C++ code in the link.

Before posting my questions, first let me show you how I did set up a
VS2005 C++ project to test this code.

To create a test project, I do following

File->New->Project->(Other Languages)->Visaul C++->CLR->Class Library

Fill in solution name and put in the following code.

----------------------------------------------- TestAsynCallback.h
-----------------------------------------
namespace TestAsynCallback {
public ref class UdpState
{

public:
UdpState (void) {};

IPEndPoint^ ipEndPoint;
UdpClient^ udpClient;
};

public ref class Class1
{
// TODO: Add your methods for this class here.


public:
Class1(void)
{

};

bool isMessageReceived;

void ReceiveCallback(IAsyncResult^ asyncResult);

void ReceiveMessages();

};
}

---------------------------------------------------TestAsynCallback.cpp
-------------------------------------
// This is the main DLL file.

#include "stdafx.h"

#include "TestAsynCallback.h"

namespace TestAsynCallback
{

void Class1::ReceiveCallback(IAsyncResult^ asyncResult)
{
UdpClient^ udpClient =
((UdpState)(asyncResult->AsyncState)).udpClient;
IPEndPoint^ ipEndPoint =
((UdpState)(asyncResult->AsyncState)).ipEndPoint;

array<Byte>^ receiveBytes =
udpClient->EndReceive(asyncResult, ipEndPoint);
String^ receiveString =
Encoding::ASCII->GetString(receiveBytes);

Console::WriteLine("Received: {0}", receiveString);
isMessageReceived = true;
}

void Class1::ReceiveMessages()
{
// Receive a message and write it to the console.
IPEndPoint^ ipEndPoint = gcnew IPEndPoint(IPAddress::Any,
listenPort);
UdpClient^ udpClient = gcnew UdpClient(ipEndPoint);

UdpState^ udpState = gcnew UdpState();
udpState->ipEndPoint = ipEndPoint;
udpState->udpClient = udpClient;

Console::WriteLine("listening for messages");
udpClient->BeginReceive(gcnew AsyncCallback(ReceiveCallback),
udpState);

// Do some work while we wait for a message. For this example,
// we'll just sleep
while (!isMessageReceived)
{
Thread::Sleep(100);
}
}

}
-----------------------------------------------------------------------------------------------------------

Question 1)

Notice I took out key word 'static' in the header file. So instead, for
example,

static void ReceiveCallback(IAsyncResult^ asyncResult);

it becomes

void ReceiveCallback(IAsyncResult^ asyncResult);

However when I complie, I get the following error message

Error 1 error C3867: 'TestAsynCallback::Class1::ReceiveCallback':
function call missing argument list; use
'&TestAsynCallback::Class1::ReceiveCallback' to create a pointer to
member

Error 2 error C3350: 'System::TestAsyncCallback' : a delegate
constructor expects 2 argument(s)

which comes from this line of code

udpClient->BeginReceive(gcnew AsyncCallback(ReceiveCallback),
udpState);

Therefore I like to know how do I go around this problem. The reason I
have to change from static to non-static methode is because I have to
raise an event which requires passing 'this' keyword; however static
methode does not allow to do this.

Question 2)

If I leave the code intact and try to complie, I get the following
error.

Error 1 error C2440: 'type cast' : cannot convert from 'System::Object
^' to 'TestAsynCallbackTony::UdpState'

Error 2 error C2101: '&' on constant

Error 3 fatal error C1903: unable to recover from previous error(s);
stopping compilation

which comes from this line of code

UdpClient^ udpClient =
((UdpState)(asyncResult->AsyncState)).udpClient;

And I have no clue how to fix it.

I wonder what have I done wrong or these errors could be resulted from
complier bugs.

Any help from anyone will be greatly appreciated.

TC
 
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