How to define lParam for COPYDATASTRUCT?

Question

So I kinda followed this :

https://msdn.microsoft.com/en-us/library/ms649009(v=vs.85).aspx

and this:

Use WM_COPYDATA to send data between processes

For sending data between a openframeworks application and unreal engine 4. Now everything seems to be fine, except I cant seem to find why I am getting an error that lParam is undefined. It's probably something simple, but I cant find how to do it.

So in unreal engine 4 I have an actor which send a message every 10 sec (for test purposes):

void ACOMActor::Tick( float DeltaTime )
{
    Super::Tick( DeltaTime );

    timer += DeltaTime;

    if (timer > sendtime) {
        timer = 0.f;
        std::string string  = "a message";
        const wchar_t* wstring = new wchar_t[string.length() +1];
        std::copy(string.begin(), string.end(), wstring);
        SendWMCOPYDATA(wstring);
    }
}

void ACOMActor::SendWMCOPYDATA(const wchar_t* string)
{
    HWND WINAPI GetActiveWindow(void);
    LPCTSTR lpszString = string;
    COPYDATASTRUCT cds;
    cds.dwData = 1;
    cds.cbData = sizeof(TCHAR) * (_tcslen(lpszString) + 1);
    cds.lpData = &lpszString;

    SendMessage(GetActiveWindow(), WM_COPYDATA, (WPARAM)GetActiveWindow(), (LPARAM)(LPVOID)&cds);

    GEngine->AddOnScreenDebugMessage(-1, 5.F, FColor::Green, FString::Printf(TEXT("Sending a message")));
}

Some code is still a bit rough but I was just trying to get it to work first.

I also created code for receiving the message in openframeworks. I wasn't exactly sure how to do this so I added this to the update function of my ofApp.cpp

void ofApp::update() {
    GM->update();

    PCOPYDATASTRUCT pMyCDS;
    void WINAPI MyDisplay(LPSTR, LPSTR, DWORD);

    pMyCDS = (PCOPYDATASTRUCT)lParam;
    if (pMyCDS->dwData == 1)
    {
        LPCTSTR lpszString = (LPCTSTR)(pMyCDS->lpData);
        cout << "receiving a message" << endl;
    }
}

So this doesn't work, because lParam is undefined. I also tried to do something with LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)

But I am unfamiliar with this and I am not sure how to use it. My error was gone but the message was not received... I used it like this, wrong probably:

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PCOPYDATASTRUCT pMyCDS;
    void WINAPI MyDisplay(LPSTR, LPSTR, DWORD);
    pMyCDS = (PCOPYDATASTRUCT)lParam;
    if (pMyCDS->dwData == 1)
    {
        LPCTSTR lpszString = (LPCTSTR)(pMyCDS->lpData);
        cout << "receiving a message" << endl;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}

Any tips how to achieve this? It is probably really simple but I can't find any clear information. Thanks!

There are too many things wrong, starting with GetActiveWindow(). That only ever works by accident, it never works across processes. Just don't, use a named pipe instead. — Hans Passant, Mar 01 '16 at 12:23
With a named pipe, do you mean this?: https://msdn.microsoft.com/en-us/library/aa365574(v=vs.85).aspx#base.using_pipes_for_ipc — Alexander S., Mar 01 '16 at 13:20

How to define lParam for COPYDATASTRUCT?

0 Answers0