How can I convert BITMAPINFOHEADER into Byte array using c++

Question

I wish to convert a BITMAPINFOHEADER into a byte array to send it over a TCP socket connection. I can capture the Desktop screen, and the image is in a BITMAPINFOHEADER. Below is the code I have tried:

void CaptureAndSendScreen()
{
    HDC hdcScreen;
    HDC hdcWindow;
    HDC hdcMemDC = NULL;
    HBITMAP hbmScreen = NULL;
    BITMAP bmpScreen;

    HWND hWnd = GetDesktopWindow();

    // 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, "StretchBlt has failed","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, "CreateCompatibleBitmap Failed","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, "BitBlt has failed", "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);

    // **need to convert bi into Byte array and send through TCP socket**

    //Unlock and Free the DIB from the heap
    GlobalUnlock(hDIB);    
    GlobalFree(hDIB);

//Clean up
done:
    DeleteObject(hbmScreen);
    DeleteObject(hdcMemDC);
    ReleaseDC(NULL,hdcScreen);
    ReleaseDC(hWnd,hdcWindow);
}

Answer 1

You don't need to convert it. The send() socket function takes a pointer to an arbitrary memory buffer, thus you can send the BITMAPINFOHEADER and pixel data as-is. The only caveat is send() expects a char* pointer, but you can just use a type-cast for that, eg:

send(theSocket, (char*)&bi, sizeof(bi), 0);
send(theSocket, lpbitmap, dwBmpSize, 0);