Serialize: CArchive a CImage - c++

Question

I am currently trying to figure out how to properly store a CImage file within a CArchive (JPEG). My current approach to this is the following (pseudo) code:
BOOL CPicture::Serialize(CArchive &ar)
{
IStream *pStream = NULL;
HRESULT hr;
CImage *img = GetImage();
if (ar.IsLoading())
{
HGLOBAL hMem = GlobalAlloc(GMEM_FIXED, 54262);
hr = CreateStreamOnHGlobal(hMem, FALSE, &pStream);
if(SUCCEEDED(hr))
{
ar.Read(pStream, 54262);
img->Load(pStream);
pStream->Release();
GlobalUnlock(hMem);
GlobalFree(hMem);
}
}
else
{
hr = CreateStreamOnHGlobal(0, TRUE, &pStream);
if (SUCCEEDED(hr))
{
hr = img->Save(pStream, Gdiplus::ImageFormatJPEG);
if (SUCCEEDED(hr))
ar.Write(pStream, 54262);
}
}
...
I am just now getting back into C++ and have only done a little with it in the past. Any help would be very much appreciated.
Thank you very much in advance.

Answer 1

I'm not an expert on IStream, but I think you may not be using it correctly. The following code seems to work. It currently archives in png format, but it can easily be changed through Gdiplus::ImageFormatPNG.
It owes a lot to the tutorial "Embracing IStream as just a stream of bytes" by S. Arman on CodeProject.
void ImageArchive(CImage *pImage, CArchive &ar)
{
HRESULT hr;
if (ar.IsStoring())
{
// create a stream
IStream *pStream = SHCreateMemStream(NULL, 0);
ASSERT(pStream != NULL);
if (pStream == NULL)
return;
// write the image to a stream rather than file (the stream in this case is just a chunk of memory automatically allocated by the stream itself)
pImage->Save(pStream, Gdiplus::ImageFormatPNG); // Note: IStream will automatically grow up as necessary.
// find the size of memory written (i.e. the image file size)
STATSTG statsg;
hr = pStream->Stat(&statsg, STATFLAG_NONAME);
ASSERT(hr == S_OK);
ASSERT(statsg.cbSize.QuadPart < ULONG_MAX);
ULONG nImgBytes = ULONG(statsg.cbSize.QuadPart); // any image that can be displayed had better not have more than MAX_ULONG bytes
// go to the start of the stream
LARGE_INTEGER seekPos;
seekPos.QuadPart = 0;
hr = pStream->Seek(seekPos, STREAM_SEEK_SET, NULL);
ASSERT(hr == S_OK);
// get data in stream into a standard byte array
char *bytes = new char[nImgBytes];
ULONG nRead;
hr = pStream->Read(bytes, nImgBytes, &nRead); // read the data from the stream into normal memory. nRead should be equal to statsg.cbSize.QuadPart.
ASSERT(hr == S_OK);
ASSERT(nImgBytes == nRead);
// write data to archive and finish
ar << nRead; // need to save the amount of memory needed for the file, since we will need to read this amount later
ar.Write(bytes, nRead); // write the data to the archive file from the stream memory
pStream->Release();
delete[] bytes;
}
else
{
// get the data from the archive
ULONG nBytes;
ar >> nBytes;
char *bytes = new char[nBytes]; // ordinary memory to hold data from archive file
UINT nBytesRead = ar.Read(bytes, nBytes); // read the data from the archive file
ASSERT(nBytesRead == UINT(nBytes));
// make the stream
IStream *pStream = SHCreateMemStream(NULL, 0);
ASSERT(pStream != NULL);
if (pStream == NULL)
return;
// put the archive data into the stream
ULONG nBytesWritten;
pStream->Write(bytes, nBytes, &nBytesWritten);
ASSERT(nBytes == nBytesWritten);
if (nBytes != nBytesWritten)
return;
// go to the start of the stream
LARGE_INTEGER seekPos;
seekPos.QuadPart = 0;
hr = pStream->Seek(seekPos, STREAM_SEEK_SET, NULL);
ASSERT(hr == S_OK);
// load the stream into CImage and finish
pImage->Load(pStream); // pass the archive data to CImage
pStream->Release();
delete[] bytes;
}
}