CreateWindowEx - GetLastError() = 6

Ok if I've done this once I've done it a million bloody times. The only difference here is I'm calling CreateWindowEx() passing parameters which are parameters of a function in a DLL:

Code:

---

HWND GFXBase::NewWindow(HINSTANCE hInst, WNDPROC wndProc, DWORD windowStyle,
                        char *className, char *windowTitle, int x, int y, int width, int height)
{
    this->mWindowInstance = hInst;
    DWORD lastError = NULL;
    char buf[120] = {0};

    mWC.cbClsExtra = 0;
    mWC.cbSize = sizeof(mWC);
    mWC.cbWndExtra = 0;
    mWC.hbrBackground = reinterpret_cast<HBRUSH> (COLOR_WINDOW);
    mWC.hCursor = LoadCursor(NULL, IDC_ARROW);
    mWC.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    mWC.hIconSm = LoadIcon(NULL, IDI_APPLICATION);
    mWC.hInstance = hInst;
    mWC.lpfnWndProc = wndProc;
    mWC.lpszClassName = className;
    mWC.lpszMenuName = NULL;
    mWC.style = CS_HREDRAW | CS_VREDRAW;

    if (! RegisterClassEx(&mWC))
    {
        lastError = GetLastError();
        sprintf(buf, "Unable to register window class [%u]", lastError);
        MessageBox(NULL, buf, "GFXBase::NewWindow",
                  MB_OK | MB_ICONERROR | MB_TASKMODAL);
        return NULL;
    }

    this->mWindowHandle = CreateWindowEx(NULL, className, windowTitle, windowStyle,
                                      x, y, width, height, NULL, NULL, NULL, NULL);
    if (! this->mWindowHandle)
    {
        lastError = GetLastError();
        sprintf(buf, "Unable to create window [%u]", lastError);
        MessageBox(NULL, buf, "GFXBase::NewWindow",
                  MB_OK | MB_ICONERROR | MB_TASKMODAL);
        return NULL;
    }

    return this->mWindowHandle;
}

---

The above is in the DLL. This calls it:

Code:

---

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    GFXBase *gfxBase = GFXBase::CreateInstance();
    HWND hWnd = NULL;
    MSG msg;

    hWnd = gfxBase->NewWindow(hInstance, WndProc, WS_OVERLAPPEDWINDOW, "GFXBaseClient", "GFXBase Sandbox",
                              0, 0, 320, 240);

    if (! hWnd)
    {
        gfxBase->DestroyWindow();
        GFXBase::FreeInstance();
        return 1;
    }

    while (GetMessage(&msg, hWnd, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    gfxBase->DestroyWindow();
    GFXBase::FreeInstance();
    return 0;
}

---

Now I've debugged it to death and the parameters are coming through to NewWindow fine and when I step down to the CreateWindowEx call they remain unchanged. Still, it fails with GetLastError() returning 6 ("The Handle is invalid"). Which handle? It takes 3 and none of them apply here so they should be NULL. Right?

Well the first param to CreateWindowEx, dwExStyle, shouldn't be NULL (it's asking for a value dude, not a pointer), try 0.

Then there's the little matter of hInstance, the second-to-last param. That can't be NULL otherwise it can't attribute the window to any process. Try GetModuleHandle(NULL).

Well my compiler #define's NULL as 0 and according to MSDN, under XP that hInstance parameter is ignored.

I'll try them though.

Nope same problem. Blasted 6.

Try:

Code:

---

    mWC.hbrBackground = reinterpret_cast<HBRUSH> (COLOR_WINDOW + 1);
    mWC.hCursor = LoadCursor(NULL, IDC_ARROW);
    mWC.hIcon = LoadIcon(NULL, IDI_APPLICATION);
    mWC.hIconSm = NULL

---

Nope still the same error code. I don't know what in the ........ I'm doing wrong. I just knocked up a small windows program w/o using a DLL and had the same problem.

I bet it's something glaringly obvious too.

Okay then, what does wndProc return after handling WM_CREATE?

It returns 0.

Code:

---

LRESULT CALLBACK WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
    switch (uMsg)
    {
    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    case WM_CREATE:
        break;
    }

    return 0;
}

---

It's not a dialog box, so you need to have:

Code:

---

default:
    return DefWindowProc(hWnd, uMsg, wParam, lParam);

---

As a case in your WindowProc, otherwise WM_NCCREATE isn't handled properly and CreateWindowEx assumes the worst.

I can't believe I forgot about DefWindowProc(). Cheers SMurf-o!