C++ Take a Screenshot [closed] - c++

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I'm new to C++ and have to take a screenshot. I think I have set up everything besides the print method itself and that's where I'm struggling.
I found a post on so which describes how to take a screenshot, but it somehow doesn't work for me. (How to capture part of the screen and save it to a BMP?)
My Method looks like this:
STDOVERRIDEMETHODIMP VImplPrintable::Print(HDC hdc, CRect* pCr)
{
HDC hdcSource = GetDC(NULL);
HDC hdcMemory = CreateCompatibleDC(hdcSource);
int capX = GetDeviceCaps(hdcSource, HORZRES);
int capY = GetDeviceCaps(hdcSource, VERTRES);
HBITMAP hBitmap = CreateCompatibleBitmap(hdcSource, pCr->Width(), pCr->Height());
HBITMAP hBitmapOld = (HBITMAP)SelectObject(hdcMemory, hBitmap);
BitBlt(hdcMemory, 0, 0, pCr->Width(), pCr->Height(), hdcSource, pCr->top, pCr->left, SRCCOPY);
DeleteDC(hdcSource);
DeleteDC(hdcMemory);
return S_OK;
}
Problem is the screenshot seems to be an empty bitmap.
I don't really know if I it makes sense to create a new HDC when I'm
already getting one as a parameter. Any help is appreciated.

Answer 1

I cannot test because I do not know what is the framework that calls that method, but as you receive the HDC you want to write to, you simply should not use a memory DC and directly BitBlt there. But you should also test the return value of WinAPI calls to return error conditions to the caller:
STDOVERRIDEMETHODIMP VImplPrintable::Print(HDC hdc, CRect* pCr)
{
HDC hdcSource = GetDC(NULL);
if (NULL == hdcSource) return E_FAIL;
HRESUL cr = S_OK;
if (!BitBlt(hdc, 0, 0, pCr->Width(), pCr->Height(), hdcSource, pCr->top, pCr->left,
SRCCOPY)) cr = E_FAIL;
DeleteDC(hdcSource);
return cr;
}