How to communicate between two different app using SendMessage API?

Anasuya2015

How to communicate between two different app using Send Message API? Ex: APP1 having textbox txtBox1 APP2 having textbox txtBox2 In txtbox1 whats ever we type, that needs to be displayed in textbox2. How to achieve it using SendMessage() API. Ex code in VC++ is appreciated.

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!