Save a PNG to a stream

Cliff <>
Mon, 22 Sep 2008 12:31:34 -0700 (PDT)
I can't figure out what is wrong with the following function. It is
supposed to take the given image object and use it to save the image
it contains to a stream. The information from the stream will be
transferred to an HGLOBAL for the calling function to use.

All of the above really doesn't matter. I just thought I would fill
you in. The problem is that the function works fine on a jpeg format
(indicated by the encoder parameter) however if I pass in "image/png"
for the encoder value, the image will not save. It fails and sometimes
I get a value of 10 (file not found) or "undefined value" in the
Status variable. I'm completely stuck on this. My boss still insists
on using c++ and mfc, and most all documentation I've found on GDI+
has been in the form of .net and c#

If you have any idea your help would be greatly appreciated.

HGLOBAL GetImageBlob(Image *pImage, CString encoder)
    IStream *imageStream;
    HRESULT hr = ::CreateStreamOnHGlobal (NULL, FALSE, &imageStream);
    CLSID clsid;
    GetEncoderClsid((WCHAR *) encoder.GetString(), &clsid);
    Status s = pImage->Save(imageStream, &clsid);//Problem
    STATSTG stats;
    imageStream->Stat(&stats, 0);
    unsigned char *pBuf = (unsigned char *) GlobalLock(hBuf);

    disp.QuadPart = 0;
    unsigned long read = 0;
    imageStream->Seek(disp, STREAM_SEEK_SET, NULL);
    imageStream->Read(pBuf, stats.cbSize.QuadPart, &read);
    return hBuf;

//Helper function found on that is supposed to get the class
id of the requested image encoder.
int GetEncoderClsid(const WCHAR* format, CLSID* pClsid)
   UINT num = 0; // number of image encoders
   UINT size = 0; // size of the image encoder array in bytes

   ImageCodecInfo* pImageCodecInfo = NULL;

   GetImageEncodersSize(&num, &size);
   if(size == 0)
      return -1; // Failure

   pImageCodecInfo = (ImageCodecInfo*)(malloc(size));
   if(pImageCodecInfo == NULL)
      return -1; // Failure

   GetImageEncoders(num, size, pImageCodecInfo);

   for(UINT j = 0; j < num; ++j)
      if( wcscmp(pImageCodecInfo[j].MimeType, format) == 0 )
         *pClsid = pImageCodecInfo[j].Clsid;
         return j; // Success

   return -1; // Failure

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