How to communicate between two different app using SendMessage API?

[Lost User]

See SendMessage function (Windows)[^]. Use the RegisterWindowMessage function (Windows)[^] to create a message number that is unique to your applications, and set the other two parameters to values that both your applications understand.

[Anasuya2015]

Thanks for your help. I am facing issue in extracting the message. Code is as follows... APP1:

int WM_MYMSG = RegisterWindowMessage (L"MYMESSAGE");
HWND hw = FindWindow(NULL, L"Demo");
LPCTSTR strMsg = L"ClientDemo1";
//Send that message
::SendMessage(hw, WM_MYMSG, NULL, (LPARAM(LPCTSTR)strMsg);

APP2:

LRESULT CDemoDlg::OnMyMsg(WPARAM w, LPARAM l) {

MSG\* p = (MSG\*)l;
LPCTSTR str = (LPCTSTR)p->message;
MessageBox(str);// No message. But getting the alert while sending message. Need to extract the actual msg here.

return (LRESULT) 0;

}

Please let me know what changes is needed here by which it'll display "ClientDemo1" in msgbox.

[Lost User]

The LPARAM in your sending application is a Unicode string, so why are you casting it to a MSG pointer in the receiving app?

[Arthur V Ratz]

You can use COM automation, Named Pipes, TCP/IP Sockets or whatsoever by implementing your own protocol for interprocess communtication. :)

[Anasuya2015]

I am just finding the way to print the message. So you mean to say it is not needed and directly we can use lparam to print the message?

[Anasuya2015]

Here requirement is restrict to SendMessage() API. Anyway thanks for your answer. Can you send any sample code for Named Pipes implementation?

[Arthur V Ratz]

Using Pipes - MSDN Resource

[Lost User]

Anasuya2015 wrote:

So you mean to say ...

No, I am saying that whatever type you use in the LPARAM field in the sending app, you must use the same type in the receiver.

[Arthur V Ratz]

Also you can reuse SendMessage() API function with its regular list of arguments by implementing your own that encapsulates for example named pipes client mechanism. :)

[Serkan Onat]

You can use WM_COPYDATA[^] message with SendMessage API There is a linked example on MSDN topic as well

[David Crow]

Your casting is a bit unclear. It should probably be:

::SendMessage(hw, WM_MYMSG, NULL, (LPARAM) strMsg);
...
LPCTSTR str = (LPCTSTR) l;
MessageBox(str);

The process calling SendMessage() will likely be blocked by the second process since it will be waiting on the message box to be dismissed.

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[Maximilien]

:thumbsup: This is what we use and it works nicely

I'd rather be phishing!