How do I load and save an image from an SQL Server database using GDI+ and C++?

Question

I need specifically to load a JPG image that was saved as a blob. GDI+ makes it very easy to retrieve images from files but not from databases...

Answer 1

Take a look at Image::Image(IStream *, BOOL). This takes a pointer to a COM object implementing the IStream interface. You can get one of these by allocating some global memory with GlobalAlloc and then calling CreateStreamOnHGlobal on the returned handle. It'll look something like this:

shared_ptr<Image> CreateImage(BYTE *blob, size_t blobSize)
{
    HGLOBAL hMem = ::GlobalAlloc(GMEM_MOVEABLE,blobSize);
    BYTE *pImage = (BYTE*)::GlobalLock(hMem);

    for (size_t iBlob = 0; iBlob < blobSize; ++iBlob)
        pImage[iBlob] = blob[iBlob];

    ::GlobalUnlock(hMem);

    CComPtr<IStream> spStream;
    HRESULT hr = ::CreateStreamOnHGlobal(hMem,TRUE,&spStream);

    shared_ptr<Image> image = new Image(spStream);  
    return image;
}

But with error checking and such (omitted here to make things clearer)