// get screen DC and memory DC to copy to
HDC hScreenDC = GetDC(0);
HDC hMemoryDC = CreateCompatibleDC(hScreenDC);

// create a DIB to hold the image
BITMAPINFO bmi = { 0 };
bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
bmi.bmiHeader.biWidth = GetDeviceCaps(hScreenDC, HORZRES);
bmi.bmiHeader.biHeight = -GetDeviceCaps(hScreenDC, VERTRES);
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
LPVOID pBits;
HBITMAP hBitmap = CreateDIBSection(hMemoryDC, &bmi, DIB_RGB_COLORS, &pBits, NULL, 0);

// select new bitmap into memory DC
HGDIOBJ hOldBitmap = SelectObject(hMemoryDC, hBitmap);

// copy from the screen to memory
BitBlt(hMemoryDC, 0, 0, bmi.bmiHeader.biWidth, -bmi.bmiHeader.biHeight, hScreenDC, 0, 0, SRCCOPY);

// clean up
SelectObject(hMemoryDC, hOldBitmap);
DeleteDC(hMemoryDC);
ReleaseDC(0, hScreenDC);

// the image data is now in pBits in 32-bpp format
// free this when finished using DeleteObject(hBitmap);