title: C++: Hbitmap/BITMAP into .bmp file
body: <p>Ok, whole story is, I am trying to use Leptonica+Tesseract OCR in C++ to take a screenshot, save it to a *.bmp file, then load it back up to OCR with it. I won't need to do this frequently, but as I cannot seem to copy the screenshot data directly into a Leptonica PIX structure, I need to save it to a file first..actually a solution to this would be preferably.</p>
  
  <p>Here's some code I've found online, trying to help me out. </p>
  
  <p>Screen cap:</p>
  
  <pre><code>HBITMAP ScreenCapture(){
    int width=100;
    int height=100;
    // get the device context of the screen
    HDC hScreenDC = CreateDC(L"DISPLAY", NULL, NULL, NULL);     
    // and a device context to put it in
    HDC hMemoryDC = CreateCompatibleDC(hScreenDC);
  
    int x = GetDeviceCaps(hScreenDC, HORZRES);
    int y = GetDeviceCaps(hScreenDC, VERTRES);
  
    // maybe worth checking these are positive values
    HBITMAP hBitmap = CreateCompatibleBitmap(hScreenDC, x, y);
  
    // get a new bitmap
    HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemoryDC, hBitmap);
  
    BitBlt(hMemoryDC, 0, 0, width, height, hScreenDC, 0, 0, SRCCOPY);
    hBitmap = (HBITMAP)SelectObject(hMemoryDC, hOldBitmap);
  
    //GlobalAlloc(GPTR, hBitmap)
  
    WriteDIB(L"test.bmp", (HGLOBAL)hBitmap);
  
    // clean up
    DeleteDC(hMemoryDC);
    DeleteDC(hScreenDC);
  
    return hBitmap;
    // now your image is held in hBitmap. You can save it or do whatever with it
  }
  </code></pre>
  
  <p>Attempt to write function: </p>
  
  <pre><code>BOOL WriteDIB( LPTSTR szFile, HANDLE hDIB)
  {
    cout&lt;&lt;endl&lt;&lt;"Running save function";
    /*HANDLE hDIB=GlobalAlloc(GPTR, sizeof(hDIBtochange));//this doesn't work, the result is four. Also the HANDLE parameter's name would be changed to hDIBtochange, so that the rest of the function uses the old 'hDIB' throughout
    cout&lt;&lt;endl&lt;&lt;sizeof(hDIBtochange);*/
    BITMAPFILEHEADER  hdr;
    LPBITMAPINFOHEADER    lpbi;
    if (!hDIB)
      return FALSE;
    CFile file;
    if( !file.Open( szFile, CFile::modeWrite|CFile::modeCreate) )
      return FALSE;
    lpbi = (LPBITMAPINFOHEADER)hDIB;
    int nColors = 1 &lt;&lt; lpbi-&gt;biBitCount;
    // Fill in the fields of the file header 
    hdr.bfType        = ((WORD) ('M' &lt;&lt; 8) | 'B');    // is always "BM"
    hdr.bfSize        = GlobalSize (hDIB) + sizeof( hdr );
    hdr.bfReserved1   = 0;
    hdr.bfReserved2   = 0;
    hdr.bfOffBits     = (DWORD) (sizeof( hdr ) + lpbi-&gt;biSize + nColors * sizeof(RGBQUAD));
    // Write the file header 
    file.Write( &amp;hdr, sizeof(hdr) );
    // Write the DIB header and the bits 
    file.Write( lpbi, GlobalSize(hDIB) );
    return TRUE;
  }
  </code></pre>
  
  <p>Shamelessly copied from people's posts over the years.
  Ok! Problem I face is, I cannot seem to understand how to GlobalAlloc the Hbitmap into a globally accessible Handle, that can be converted or use with LPBITMAPINFOHEADER.
  Soon as lpbi is created, every single field inside of it is "Unable to read memory" error in Visual Studio 2012 debugging. It's inaccessible, despite being created.</p>
  
  <p>Solutions..
  Go straight from screencap to PIX, inside of memory..
  Find a way to save to bitmap and create them periodically to read..
  Find another way entirely that makes more sense..</p>
  
  <p>Preferring first, but, I'm asking for a solution in this, to the second one..or third.</p>
  
  <p>If you need more info I can try to provide it. This mostly boils down to "I've never done code like this before and it wasn't taught in my classes so I'm trying to learn as I go".</p>