HDC memory leak (release HDC/ delete hdc)

Question

I'm having trouble with this HDC memory leak. Could you guys check if I'm releasing/deleting HDC correctly?

Thank you!

BITMAP bm;
HBITMAP hbmap;
HBITMAP hBitmapOld;
BITMAPINFO bmi;
HDC hdcShot;

...

while(true)
{
    if (!TakeScreenshot(GameWindow, bm, hbmap, bmi, hdcShot, hBitmapOld, appWnd))
                    break;

        HBITMAP hbmapNew = CreateCompatibleBitmap(hdcShot, rcWindow.right - rcWindow.left, rcWindow.bottom - rcWindow.top);

        HDC hdcShotNew = CreateCompatibleDC(hdcShot);

        HBITMAP OldBmp = (HBITMAP)SelectObject(hdcShotNew, hbmapNew);


        BitBlt(hdcShotNew, 0, 0, rcWindow.right - rcWindow.left/*Window WIDTH*/, rcWindow.bottom - rcWindow.top/*Window HEIGHT*/
            , hdcShot, 0, 0, SRCCOPY);


        pPixels = new RGBQUAD[bm.bmWidth * bm.bmHeight];
        if (!pPixels) return false;

        SelectObject(hdcShotNew, OldBmp);


        if (!GetDIBits(hdcShotNew, hbmapNew, 0, bm.bmHeight, pPixels, &bmi, DIB_RGB_COLORS))
        {
            DeleteDC(hdcShot);
            delete[] pPixels;

            return false;
        }



// dont mind about this
        ScanContents scanContentsMain(bm, rcWindow, pPixels);
// dont mind about this
        ScanBMPHorizontal(&scanContentsMain);




        //free memory - I might have cleared the memory incorrectly here! Please check!
        free(pPixels);
        SelectObject(hdcShot, hBitmapOld);
                DeleteDC(hdcShot);
                DeleteObject(hbmapNew);
                DeleteDC(hdcShotNew);
}

TakeScreenShot Func (not really important but it shows how some variables are initialized)

    bool TakeScreenshot(std::string WindowToFind, BITMAP &bm, HBITMAP &hbmap, BITMAPINFO &bmi, HDC &hdcShot, HBITMAP &hBitmapOld, HWND &hwnd)
{
    RECT rc;
    GetWindowRect(hwnd, &rc);
    hdcShot = CreateCompatibleDC(0);
    hbmap = CreateCompatibleBitmap(GetDC(0), rc.right - rc.left/*Window WIDTH*/, rc.bottom - rc.top/*Window HEIGHT*/);

    SelectObject(hdcShot, hbmap);


    BitBlt(hdcShot, 0, 0, rc.right - rc.left/*Window WIDTH*/, rc.bottom - rc.top/*Window HEIGHT*/
        , GetDC(0), rc.left, rc.top, SRCCOPY);

//Ignore this
    if (!GetObject(hbmap, sizeof(BITMAP), (LPSTR)&bm))
        return false;
    int bitsPerPixel = bm.bmBitsPixel;


 //Ignore this  
    if (bitsPerPixel != 32 || bm.bmPlanes != 1)
        return false;

//Don't mind about this too much 
    SetupBitmapInfo(bmi, bm.bmWidth, bm.bmHeight, bitsPerPixel);


    return true;

}

I checked with deleakers and found out that I'm struggling with HDC leak. I'm not sure what I've done wrong.

Answer 1

You have a resource leak here:

hbmap = CreateCompatibleBitmap(GetDC(0), rc.right - rc.left, rc.bottom - rc.top);

You should change to

HDC hdc = GetDC(0);
CreateCompatibleBitmap(hdc, rc.right - rc.left, rc.bottom - rc.top);
... 
ReleaseDC(0, hdc);//call this before exiting the function

free(pPixels) is wrong (although it still cleans up in this case). Replace free(pPixels) with delete[]pPixels

Change this:

SelectObject(hdcShot, hBitmapOld);
DeleteDC(hdcShot);
DeleteObject(hbmapNew);
DeleteDC(hdcShotNew);

To this:

SelectObject(hdcShot, OldBmp);
DeleteObject(hbmapNew);
DeleteObject(hBitmapOld);
DeleteDC(hdcShot);
DeleteDC(hdcShotNew);