程序代码：

#include <windows.h>
#include <conio.h>

int main (void)
{
    HWND                hWnd;
    HDC                 hdc;
    HDC                 hdcWnd;
    HDC                 hdcMem;
    HBITMAP             hBmp;
    RECT                rect;
    int                 iScrWidth, iScrHeight;

    iScrWidth = GetSystemMetrics (SM_CXSCREEN);
    iScrHeight = GetSystemMetrics (SM_CYSCREEN);

    hWnd = GetForegroundWindow ();
    GetClientRect (hWnd, &rect);
    hdc = CreateDC ("DISPLAY", NULL, NULL, NULL);
  
    hdcMem = CreateCompatibleDC (hdc);
    hBmp = CreateCompatibleBitmap (hdcMem, iScrWidth, iScrHeight);
    SelectObject (hdcMem, hBmp);

    BitBlt (hdcMem, 0, 0, iScrWidth, iScrHeight, hdc, 0, 0, SRCCOPY);

    hdcWnd = GetDC (hWnd);
    BitBlt (hdcWnd, 0, 0, rect.right, rect.bottom, hdcMem, 0, 0, SRCCOPY);
    ReleaseDC (hWnd, hdcWnd);

    getch ();
    DeleteObject (hBmp);
    DeleteDC (hdcMem);
    DeleteDC (hdc);

    return 0;
}

如果不经过内存dc这个间接的过程, 直接把桌面dc贴到窗口dc上, 就可以得到预期效果, 程序如下

程序代码：

#include <windows.h>
#include <conio.h>

int main (void)
{
    HWND                hWnd;
    HDC                 hdc;
    HDC                 hdcWnd;
    RECT                rect;
    int                 iScrWidth, iScrHeight;

    iScrWidth = GetSystemMetrics (SM_CXSCREEN);
    iScrHeight = GetSystemMetrics (SM_CYSCREEN);

    hWnd = GetForegroundWindow ();
    GetClientRect (hWnd, &rect);
    hdc = CreateDC ("DISPLAY", NULL, NULL, NULL);
    hdcWnd = GetDC (hWnd);

    BitBlt (hdcWnd, 0, 0, rect.right, rect.bottom, hdc, 0, 0, SRCCOPY);

    getch ();
    ReleaseDC (hWnd, hdcWnd);
    DeleteDC (hdc);

    return 0;
}