// this function create a bmp file to save the current screen;
// supported eVC++ 4.0 (wince 4.0) and vc++ 6.0 , test pass; 
void CSnapDlg::OnScreenSave(const char *filename)
{ 
    HDC  hScrDC, hMemDC;         
    int  width, height; 
 
 //the pointer will save all pixel point's color value
 BYTE  *lpBitmapBits = NULL; 
        
 //creates a device context for the screen device
    hScrDC = CreateDC(_T("DISPLAY"), NULL, NULL, NULL);

//get the screen point size
    width = GetDeviceCaps(hScrDC, HORZRES);
    height = GetDeviceCaps(hScrDC, VERTRES);

//creates a memory device context (DC) compatible with the screen device(hScrDC)  
    hMemDC = CreateCompatibleDC(hScrDC);

 //initialise the struct BITMAPINFO for the bimap infomation， 
 //in order to use the function CreateDIBSection
 // on wince os, each pixel stored by 24 bits(biBitCount=24) 
 //and no compressing(biCompression=0) 
    BITMAPINFO RGB24BitsBITMAPINFO; 
    ZeroMemory(&RGB24BitsBITMAPINFO, sizeof(BITMAPINFO));
    RGB24BitsBITMAPINFO.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
    RGB24BitsBITMAPINFO.bmiHeader.biWidth = width;
    RGB24BitsBITMAPINFO.bmiHeader.biHeight = height;
    RGB24BitsBITMAPINFO.bmiHeader.biPlanes = 1;
    RGB24BitsBITMAPINFO.bmiHeader.biBitCount = 24;
   
  //use the function CreateDIBSection and SelectObject 
 //in order to get the bimap pointer : lpBitmapBits 
    HBITMAP directBmp = CreateDIBSection(hMemDC, (BITMAPINFO*)&RGB24BitsBITMAPINFO, 
       DIB_RGB_COLORS, (void **)&lpBitmapBits, NULL, 0);
 HGDIOBJ previousObject = SelectObject(hMemDC, directBmp);

// copy the screen dc to the memory dc
 BitBlt(hMemDC, 0, 0, width, height, hScrDC, 0, 0, SRCCOPY);
 
 //if you only want to get the every pixel color value, 
 //you can begin here and the following part of this function will be unuseful;
 //the following part is in order to write file;

 //bimap file header in order to write bmp file 
 BITMAPFILEHEADER bmBITMAPFILEHEADER;
 ZeroMemory(&bmBITMAPFILEHEADER, sizeof(BITMAPFILEHEADER));
 bmBITMAPFILEHEADER.bfType = 0x4d42;  //bmp  
    bmBITMAPFILEHEADER.bfOffBits = sizeof(BITMAPFILEHEADER) + sizeof(BITMAPINFOHEADER);
    bmBITMAPFILEHEADER.bfSize = bmBITMAPFILEHEADER.bfOffBits + ((width*height)*3); ///3=(24 / 8)
 
 //write into file
 FILE *mStream = NULL;
 if((mStream = fopen(filename, "wb")))
 {  
  //write bitmap file header
  fwrite(&bmBITMAPFILEHEADER, sizeof(BITMAPFILEHEADER), 1, mStream);
  //write bitmap info
  fwrite(&(RGB24BitsBITMAPINFO.bmiHeader), sizeof(BITMAPINFOHEADER), 1, mStream);
  //write bitmap pixels data
  fwrite(lpBitmapBits, 3*width*height, 1, mStream);
   //close file
  fclose(mStream);
 }
 
 //delete
 DeleteObject(hMemDC);
 DeleteObject(hScrDC);
 DeleteObject(directBmp);
 DeleteObject(previousObject);
}