Sending a packet using PostMessage

Stefan Pedersen

WM_COPYDATA[^] might fit your needs. And if the paths that I have followed/have tread against the flow/there is no need for sorrow I am coming home Return, Crüxshadows

Gary R Wheeler

I'm going to assume you are asking how you should use PostMessage to send a packet of information. "Which type of message" you should send depends on what you are trying to accomplish, which you haven't described. I'm also going to assume you are using MFC, and that you are trying to send a packet to a window created by your application. If you are using PostMessage(), the message is placed on the window's message queue, and PostMessage() returns immediately. The window that receives the message may take some time before it processes the message. This means that the message will have to persist until the window gets around to looking at it. The easiest way to do this is to allocate your 'packet' on the heap, and deallocate it in the message handler. Here's an example:

#define MY_MESSAGE (WM_APP + 1)

class Packet {
public:
Packet();
~Packet();
// ... data members
int m1;
};

...

// allocate a packet, set its contents

Packet *packet = new Packet;
packet->m1 = 123456;

// here's how you post a message

CString strWndName = "My wnd";
CString strClassName = "Wnd class";
HWND hwnd = ::FindWindow(strClassName,strWndName);

::PostMessage(hwnd,MY_MESSAGE,0,(LPARAM)packet);

This code sends your user-defined message MY_MESSAGE to the window with handle hwnd. Your handler for this message should be declared as follows:

afx_msg LRESULT OnMyMessage(WPARAM wParam,LPARAM lParam);

and it's implementation will look like the following:

BEGIN_MESSAGE_MAP( MyWindowClass, <window base class> )
...
ON_MESSAGE(MY_MESSAGE,OnMyMessage)
END_MESSAGE_MAP()
...

LRESULT MyWindowClass::OnMyMessage(WPARAM wParam,LPARAM lParam)
{
Packet *packet = (Packet *)lParam;

// ... use information in packet

delete packet;

return (LRESULT)0;

}

I hope this helps. If you are trying to send messages between applications, there are other methods of interprocess communication (named pipes, sockets, and so on) that are simpler.

Software Zen: delete this;

__Cerb

Ok thanks. Let's say I want to send the 0x68 packet. COPYDATASTRUCT cds; cds.lpData = NULL; cds.cbData = 1; cds.dwData = 0x68; Would this work? And what should I send as WParam? 0? Thanks a lot for your help ~Mike

__Cerb

Actually I am trying to send a packet to an online game. That's why both your codes didn't work. Thanks anyway, I hope you can help me ~Mike

Lost User

packet to an online game? You need to send such packets to the query port of the game per UDP. What do you want to do exactly?

__Cerb

I want to send the 0x68 packet to my game. I believe the client receives packets from the game server on port 6112, if this can help. Thanks, ~Mike

Lost User

Yes, read my posting above. Sending packets to game (servers) has nothing to do with PostMessage() or SendMessage(). You need to use UDP (most games use UDP, don't know which ones use TCP). Take a look at this article and its links section. regards

Gary R Wheeler

WHOA :confused:. PostMessage() is used to send Windows messages to windows, those funny things on the screen you interactive with. The phrases 'online game', '0x68 packet', 'game server', and 'port 6112' tell me that you are trying to send a specific packet to an online game, and that the game communicates using TCP/IP sockets. That is a whole 'nother kettle of fish. For introductory articles on socket programming under Windows, try here[^], here[^], and here[^]. You will also need to know the format of the packets used by the game to communicate.

Software Zen: delete this;

__Cerb

So basically I have to create a UDP socket on my game server's ip and write my packet onto it... Am I right? Thanks, ~Mike

Gary R Wheeler

That's right. Like I mentioned in my earlier message, you'll need to know the format of the packet (how many bytes, what each byte means, and so on). Good luck.

Software Zen: delete this;