Where is the memory leak from my hdc/hbitmap?

Question

so I've noticed that part of my code leaks a lot of memory when it's called and I've tried to find out where or why it leaks but I'm at a dead end.

I've tried the Visual Studio 2017 debugger to take snapshots to find out where the leak happens but according to that there aren't any major leaks. I've also tried Deleaker which I got working once which told me I leaked HDC and HBITMAP but couldn't tell me how much memory.

The first function is the GetScreenBmp where the leak might be, but aren't I releasing everything properly? I know I'm not deleting hBitmap but I need to return that. Is that where the memory leak is?

HBITMAP GetScreenBmp(HDC hdc, int screenPositionX, int screenPositionY, int screenSizeX, int screenSizeY) {
// Get screen dimensions
int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
int nMousePositionX = 0, nMousePositionY = 0;

// Create compatible DC, create a compatible bitmap and copy the screen using BitBlt()
HDC hCaptureDC = CreateCompatibleDC(hdc);
HBITMAP hBitmap = CreateCompatibleBitmap(hdc, screenSizeX, screenSizeY);
HGDIOBJ hOld = SelectObject(hCaptureDC, hBitmap);
BOOL bOK = BitBlt(hCaptureDC, 0, 0, screenSizeX, screenSizeY, hdc, screenPositionX, screenPositionY, SRCCOPY | CAPTUREBLT);

SelectObject(hCaptureDC, hOld); // always select the previously selected object once done
DeleteObject(hOld);
DeleteDC(hCaptureDC);

return hBitmap;

The second part is this piece of code, which I'm not entirely sure if I'm deleting everything properly.

HDC hdc = GetDC(0);
    HBITMAP hBitmap = GetScreenBmp(hdc, currentSplitInformationArray.screenPositionX, currentSplitInformationArray.screenPositionY, currentSplitInformationArray.screenSizeX, currentSplitInformationArray.screenSizeY);
    BITMAPINFO MyBMInfo = { 0 };
    MyBMInfo.bmiHeader.biSize = sizeof(MyBMInfo.bmiHeader);

    // Get the BITMAPINFO structure from the bitmap
    if (0 == GetDIBits(hdc, hBitmap, 0, 0, NULL, &MyBMInfo, DIB_RGB_COLORS)) {
        MessageBox(NULL, "Resource not available\nDo you want to try again?", "Account Details", MB_ICONWARNING | MB_CANCELTRYCONTINUE | MB_DEFBUTTON2);
    }

    // create the bitmap buffer
    BYTE* lpPixels = new BYTE[MyBMInfo.bmiHeader.biSizeImage];

    // Better do this here - the original bitmap might have BI_BITFILEDS, which makes it
    // necessary to read the color table - you might not want this.
    MyBMInfo.bmiHeader.biCompression = BI_RGB;
    MyBMInfo.bmiHeader.biHeight = currentSplitInformationArray.screenSizeY * -1;

    // get the actual bitmap buffer
    if (0 == GetDIBits(hdc, hBitmap, 0, currentSplitInformationArray.screenSizeY, (LPVOID)lpPixels, &MyBMInfo, DIB_RGB_COLORS)) {
        MessageBox(NULL, "Resource not available\nDo you want to try again?", "Account Details", MB_ICONWARNING | MB_CANCELTRYCONTINUE | MB_DEFBUTTON2);
    }

    ::SendMessage(testingComparison, STM_SETIMAGE,
        (WPARAM)IMAGE_BITMAP, (LPARAM)hBitmap);

    DeleteObject(&MyBMInfo);
    DeleteObject(hBitmap);
    ReleaseDC(NULL, hdc);
    delete[] lpPixels;

I'm sorry in advance if this is something that has been answered before or if the answer is easily googable, but I've been trying for a few hours to fix it.

Answer 1

Use tools to track your leaks/allocations (btw. you didn't post how you found the leaks in the first place).

Since you are using visual studio c++ you may use the built-in tools. Basicly a combination of the these 3 lines can get the job done.

    _CrtSetDbgFlag ( _CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF );//to enable, safe to always set somewhere around program startup - on normal exit this will print whatever you leaked

    //_CrtDumpMemoryLeaks();//Dumps to see what has already been allocated

    //_CrtSetBreakAlloc(#number);//Use this to set breakpoint using the allocation number from heap dump to see where allocation takes place. If allocation happends before this line it will not work.

Answer 2

Okay I found the solution. The STM_SETIMAGE message returns the previous image and you have to handle it yourself. https://docs.microsoft.com/en-us/windows/desktop/Controls/stm-setimage

I should probably learn to better read the documentation next time, sorry for wasting everyone's time with this one.

::SendMessage(testingComparison, STM_SETIMAGE,
            (WPARAM)IMAGE_BITMAP, (LPARAM)hBitmap);

Fixed it by simply doing

HBITMAP oldBitmap = (HBITMAP)::SendMessage(testingComparison, STM_SETIMAGE,
        (WPARAM)IMAGE_BITMAP, (LPARAM)hBitmap);
    DeleteObject(oldBitmap);