[Dcmlib] [Gdcm2] Assertion failed: ReferenceCount == 0

[Mathieu Malaterre]

Hi Greg,

On Sun, Aug 31, 2008 at 4:28 AM, Greg Book <gbook at gbook.org> wrote:
> I understand the appeal to not allow objects to be allocated on the stack.
> I'm most comfortable just using something like the following:
>    Image *img = new Image();
>    delete img;

Which is *exactly* identical to doing:

  SmartPointer<Image> img = new Image;

except the syntax is a little less error prone IMHO.

> Will it be possible to use the "Image *img = reader.GetImage()" syntax in
> gdcm from now on?

You have a const reference right now, which is even better than a
pointer (no null checking required).

> I don't quite understand how to use the smartpointer in a loop though... I
> have a list of files, and I need to do some operation on all of them, so I
> would do something like the following:
>
> for (i=0;i<numfiles;i++) {
>         /* open the dicom file */
>         reader.SetFileName(filepath);
>         if (!reader.Read()) {
>             SetError(msg.Format("Dicomfile '%s' not readable -
> LoadFile->LoadDicomFilelist()",filepath.c_str()));
>             return 0;
>         }
>         image = reader.GetImage();
>
>        /* get the image data... */
>         imageDataSize = image.GetBufferLength();
>         tmpImageData = new unsigned char[imageDataSize];
>         image.GetBuffer((char*)tmpImageData);
>
>        ... etc ...
> }

Two things, unless you are using GDCM trunk (see recent bug fix in
copy/cstor of Object) you cannot do:

  Image copy = reader.GetImage();

you are stuck with a :

  const Image& ref = reader.GetImage();

Because a gdcm::ImageReader does not clean itself, you also have to
move the gdcm::ImageReader within the for loop:

which leaves you (gdcm 2.0.8) with something very ugly


  std::vector < SmartPointer<Image>> images;
  SmartPointer<Image> smartref;
  for()
  {
    ImageReader r;
    r.SetFileName( );
    r.Read(); // check return

   smartref = const_cast<gdcm::Image*>(&r.GetImage()); // very ugly
   images.push_back( smartref );
  }

I have implemented more operator in SmartPointer so the very ugly line
is now (in trunk):

   smartref = r.GetImage();

 But again as I said before copy cstor is fixed so previous code is
nice and clean:

  std::vector < Image> images;
  for()
  {
    ImageReader r;
    r.SetFileName( );
    r.Read(); // check return

   images.push_back( r.GetImage() );
  }


> How would I do the above with a smartpointer?

See above. SmartPointer are really just pointer, except they will do
something very smart in situation like:

  SmartPointer<Image> ref;
  { // begin scope
   ImageReader r;
   r.SetFileName( );
   r.Read()
   ref = r.GetImage();
  } // end scope
  ref->Print( std::cout ); // this is valid !

  You have 'transfered' ownership, nice and clean.

> -Greg
> ps - I keep posting to the dcmlib list because all my posts to the gdcm2
> list bounce back to me, even though I'm signed up for the list.
>

That's way beyond my understanding :(
Please contact the sf.net people, with a copy of the bounce email (cc
me when you have done the bug report) at:

https://sourceforge.net/projects/alexandria/support/

Thanks,
-- 
Mathieu