请教怎样打开一个24位图

[htting]

初学vc
想在mfc工程中打开一个24位图片
在网上下载了一个例子
其中file->open中只有下面一段程序
void CImageViewApp::OnFileOpen()
{
static int nIndex = 1;
char szFilter[] = "BMP Files(*.BMP)|*.BMP|All Files(*.*)|*.*||";

CPreviewFileDlg FileDlg( TRUE, NULL, NULL, OFN_HIDEREADONLY, szFilter );
FileDlg.m_ofn.nFilterIndex = (DWORD) nIndex;

if( FileDlg.DoModal() == IDOK ){
CString PathName = FileDlg.GetPathName();
PathName.MakeUpper();
OpenDocumentFile( PathName );
nIndex = (int) FileDlg.m_ofn.nFilterIndex;
}

}
照抄之后却还是打不开图，请高手指点折是为什么，怎样才能打开图呢
谢谢

[youyifang]

下面的一段代码是返回一个设备无关位图的读取位图：

HANDLE ReadDIBFile(HANDLE hFile) 
{ 
    BITMAPFILEHEADER    bmfHeader; 
    DWORD               dwBitsSize; 
    UINT                nNumColors;   // Number of colors in table 
    HANDLE              hDIB;         
    HANDLE              hDIBtmp;      // Used for GlobalRealloc() //MPB 
    LPBITMAPINFOHEADER  lpbi; 
    DWORD               offBits; 
    DWORD               dwRead; 
 
    // get length of DIB in bytes for use when reading 
 
    dwBitsSize = GetFileSize(hFile, NULL); 
 
    // Allocate memory for header & color table. We'll enlarge this 
    // memory as needed. 
 
    hDIB = GlobalAlloc(GMEM_MOVEABLE, (DWORD)(sizeof(BITMAPINFOHEADER) + 
            256 * sizeof(RGBQUAD))); 
 
    if (!hDIB) 
        return NULL; 
 
    lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDIB); 
 
    if (!lpbi)  
    { 
        GlobalFree(hDIB); 
        return NULL; 
    } 
 
    // read the BITMAPFILEHEADER from our file 
 
    if (!ReadFile(hFile, (LPBYTE)&bmfHeader, sizeof (BITMAPFILEHEADER), 
            &dwRead, NULL)) 
        goto ErrExit; 
 
    if (sizeof (BITMAPFILEHEADER) != dwRead) 
        goto ErrExit; 
 
    if (bmfHeader.bfType != 0x4d42)  // 'BM' 
        goto ErrExit; 
 
    // read the BITMAPINFOHEADER 
 
    if (!ReadFile(hFile, (LPBYTE)lpbi, sizeof(BITMAPINFOHEADER), &dwRead, 
            NULL)) 
        goto ErrExit; 
 
    if (sizeof(BITMAPINFOHEADER) != dwRead) 
        goto ErrExit; 
 
    // Check to see that it's a Windows DIB -- an OS/2 DIB would cause 
    // strange problems with the rest of the DIB API since the fields 
    // in the header are different and the color table entries are 
    // smaller. 
    // 
    // If it's not a Windows DIB (e.g. if biSize is wrong), return NULL. 
 
    if (lpbi->biSize == sizeof(BITMAPCOREHEADER)) 
        goto ErrExit; 
 
    // Now determine the size of the color table and read it.  Since the 
    // bitmap bits are offset in the file by bfOffBits, we need to do some 
    // special processing here to make sure the bits directly follow 
    // the color table (because that's the format we are susposed to pass 
    // back) 
 
    if (!(nNumColors = (UINT)lpbi->biClrUsed)) 
    { 
        // no color table for 24-bit, default size otherwise 
 
        if (lpbi->biBitCount != 24) 
            nNumColors = 1 << lpbi->biBitCount; // standard size table 
    } 
 
    // fill in some default values if they are zero 
 
    if (lpbi->biClrUsed == 0) 
        lpbi->biClrUsed = nNumColors; 
 
    if (lpbi->biSizeImage == 0) 
    { 
        lpbi->biSizeImage = ((((lpbi->biWidth * (DWORD)lpbi->biBitCount) + 
                31) & ~31) >> 3) * lpbi->biHeight; 
    } 
 
    // get a proper-sized buffer for header, color table and bits 
 
    GlobalUnlock(hDIB); 
    hDIBtmp = GlobalReAlloc(hDIB, lpbi->biSize + nNumColors * 
            sizeof(RGBQUAD) + lpbi->biSizeImage, 0); 
 
    if (!hDIBtmp) // can't resize buffer for loading 
        goto ErrExitNoUnlock; //MPB 
    else 
        hDIB = hDIBtmp; 
 
    lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDIB); 
 
    // read the color table 
 
    ReadFile (hFile, (LPBYTE)(lpbi) + lpbi->biSize, 
            nNumColors * sizeof(RGBQUAD), &dwRead, NULL); 
 
    // offset to the bits from start of DIB header 
 
    offBits = lpbi->biSize + nNumColors * sizeof(RGBQUAD); 
 
    // If the bfOffBits field is non-zero, then the bits might *not* be 
    // directly following the color table in the file.  Use the value in 
    // bfOffBits to seek the bits. 
 
    if (bmfHeader.bfOffBits != 0L) 
        SetFilePointer(hFile, bmfHeader.bfOffBits, NULL, FILE_BEGIN); 
 
    if (ReadFile(hFile, (LPBYTE)lpbi + offBits, lpbi->biSizeImage, &dwRead, 
            NULL)) 
        goto OKExit; 
 
ErrExit: 
    GlobalUnlock(hDIB);     
 
ErrExitNoUnlock:     
    GlobalFree(hDIB); 
    return NULL; 
 
OKExit: 
    GlobalUnlock(hDIB); 
    return hDIB; 
} 

[d_bc]

楼上的把bitmap的结构介绍的很清楚了，OpenDocumentFile( PathName ); 返回CFile*，通过这个CFile的到文件handle，然后传给楼主提供的函数，就可以操作这个bitmap的内存了。


windows下可以利用APIs简单方便的操作bitmap，比如LoadBitmap(),CBitmap...