怎么动态截取屏幕

如何动态截取屏幕
我想编写一个程序，可以动态截取屏幕，不知在VC++该如何实现?

------解决方案--------------------
CDC dc;
dc.CreateDC( "DISPLAY ",NULL,NULL,NULL);

char filename[128];
memset(filename,0,sizeof(filename));

int nX = 0;
int nY = 0;
int Width=GetSystemMetrics(SM_CXSCREEN);
int Height=GetSystemMetrics(SM_CYSCREEN);

CBitmap bm;
bm.CreateCompatibleBitmap(&dc,Width,Height);
CDC tdc;
tdc.CreateCompatibleDC(&dc);
CBitmap *pOld=tdc.SelectObject(&bm);
tdc.BitBlt(0,0,Width,Height,&dc,nX,nY,SRCCOPY);
tdc.SelectObject(pOld);

BITMAP btm;
bm.GetBitmap(&btm);
DWORD size=btm.bmWidthBytes*btm.bmHeight;
LPSTR lpData=(LPSTR)GlobalAlloc(GPTR,size);

BITMAPINFOHEADER bih;
bih.biBitCount=btm.bmBitsPixel;
bih.biClrImportant=0;
bih.biClrUsed=0;
bih.biCompression=0;
bih.biHeight=btm.bmHeight;
bih.biPlanes=1;
bih.biSize=sizeof(BITMAPINFOHEADER);
bih.biSizeImage=size;
bih.biWidth=btm.bmWidth;
bih.biXPelsPerMeter=0;
bih.biYPelsPerMeter=0;

GetDIBits(tdc,bm,0,bih.biHeight,lpData,(BITMAPINFO*)&bih,DIB_RGB_COLORS);
BITMAPFILEHEADER bfh;
bfh.bfReserved1=bfh.bfReserved2=0;
bfh.bfType=((WORD)( 'M ' < < 8)| 'B ');
bfh.bfSize=54+size;
bfh.bfOffBits=54;
bm.DeleteObject();
tdc.DeleteDC();
dc.DeleteDC();
CFile bf;
if(bf.Open(csFolder,CFile::modeCreate|CFile::modeWrite)){
bf.WriteHuge(&bfh,sizeof(BITMAPFILEHEADER));
bf.WriteHuge(&bih,sizeof(BITMAPINFOHEADER));
bf.WriteHuge(lpData,size);
bf.Close();
}
else
return ;

GlobalFree(lpData);

return ;