程序代码：

位图                存放在内存中 马上就可以使用的位图  颜色深度跟当前设备对应

设备无关位图DIB     色彩表和位图数据合在一起

位图文件BMP文件     以BMP为扩展名保存在磁盘上，包括一个bitmap文件头和DIB数据 ,
                    bitmap文件头，可验证BMP文件的有效性

程序代码：

int CaptureAnImage(HWND hWnd)
{
    HDC hdcScreen;
    HDC hdcWindow;
    HDC hdcMemDC = NULL;
    HBITMAP hbmScreen = NULL;
    BITMAP bmpScreen;

    // Retrieve the handle to a display device context for the client
    // area of the window.
    hdcScreen = GetDC(NULL);
    hdcWindow = GetDC(hWnd);

    // Create a compatible DC which is used in a BitBlt from the window DC
    hdcMemDC = CreateCompatibleDC(hdcWindow); 

    if(!hdcMemDC)
    {
        MessageBox(hWnd, L"CreateCompatibleDC has failed",L"Failed", MB_OK);
        goto done;
    }

    // Get the client area for size calculation
    RECT rcClient;
    GetClientRect(hWnd, &rcClient);

    //This is the best stretch mode
    SetStretchBltMode(hdcWindow,HALFTONE);

    //The source DC is the entire screen and the destination DC is the current window (HWND)
    if(!StretchBlt(hdcWindow,
               0,0,
               rcClient.right, rcClient.bottom,
               hdcScreen,
               0,0,
               GetSystemMetrics (SM_CXSCREEN),
               GetSystemMetrics (SM_CYSCREEN),
               SRCCOPY))
    {
        MessageBox(hWnd, L"StretchBlt has failed",L"Failed", MB_OK);
        goto done;
    }
   
    // Create a compatible bitmap from the Window DC
    hbmScreen = CreateCompatibleBitmap(hdcWindow, rcClient.right-rcClient.left, rcClient.bottom-rcClient.top);
   
    if(!hbmScreen)
    {
        MessageBox(hWnd, L"CreateCompatibleBitmap Failed",L"Failed", MB_OK);
        goto done;
    }

    // Select the compatible bitmap into the compatible memory DC.
    SelectObject(hdcMemDC,hbmScreen);
   
    // Bit block transfer into our compatible memory DC.
    if(!BitBlt(hdcMemDC,
               0,0,
               rcClient.right-rcClient.left, rcClient.bottom-rcClient.top,
               hdcWindow,
               0,0,
               SRCCOPY))
    {
        MessageBox(hWnd, L"BitBlt has failed", L"Failed", MB_OK);
        goto done;
    }

    // Get the BITMAP from the HBITMAP
    GetObject(hbmScreen,sizeof(BITMAP),&bmpScreen);
    
    BITMAPFILEHEADER   bmfHeader;   
    BITMAPINFOHEADER   bi;
    
    bi.biSize = sizeof(BITMAPINFOHEADER);   
    bi.biWidth = bmpScreen.bmWidth;   
    bi.biHeight = bmpScreen.bmHeight; 
    bi.biPlanes = 1;   
    bi.biBitCount = 32;   
    bi.biCompression = BI_RGB;   
    bi.biSizeImage = 0; 
    bi.biXPelsPerMeter = 0;   
    bi.biYPelsPerMeter = 0;   
    bi.biClrUsed = 0;   
    bi.biClrImportant = 0;

    DWORD dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 * bmpScreen.bmHeight;

    // Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper functions that
    // call HeapAlloc using a handle to the process's default heap. Therefore, GlobalAlloc and LocalAlloc
    // have greater overhead than HeapAlloc.
    HANDLE hDIB = GlobalAlloc(GHND,dwBmpSize);
    char *lpbitmap = (char *)GlobalLock(hDIB);    

    // Gets the "bits" from the bitmap and copies them into a buffer
    // which is pointed to by lpbitmap.
    GetDIBits(hdcWindow, hbmScreen, 0,
        (UINT)bmpScreen.bmHeight,
        lpbitmap,
        (BITMAPINFO *)&bi, DIB_RGB_COLORS);

    // A file is created, this is where we will save the screen capture.
    HANDLE hFile = CreateFile(L"captureqwsx.bmp",
        GENERIC_WRITE,
        0,
        NULL,
        CREATE_ALWAYS,
        FILE_ATTRIBUTE_NORMAL, NULL);  
   
    // Add the size of the headers to the size of the bitmap to get the total file size
    DWORD dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);

    //Offset to where the actual bitmap bits start.
    bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) + (DWORD)sizeof(BITMAPINFOHEADER);
   
    //Size of the file
    bmfHeader.bfSize = dwSizeofDIB;
   
    //bfType must always be BM for Bitmaps
    bmfHeader.bfType = 0x4D42; //BM  

    DWORD dwBytesWritten = 0;
    WriteFile(hFile, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);
    WriteFile(hFile, (LPSTR)&bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);
    WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);
   
    //Unlock and Free the DIB from the heap
    GlobalUnlock(hDIB);   
    GlobalFree(hDIB);

    //Close the handle for the file that was created
    CloseHandle(hFile);
      
    //Clean up
done:
    DeleteObject(hbmScreen);
    DeleteObject(hdcMemDC);
    ReleaseDC(NULL,hdcScreen);
    ReleaseDC(hWnd,hdcWindow);

    return 0;
}