Question

I’m trying to use shared_ptr for the first time here, but I’m having some trouble doing this.

I want to get am IplImage every frame and allocate to a shared_ptr class member, releasing the last image. It’s something like this:

class Detector {
public: 
       void Detector::updateImage {
            main_image_.reset(cvCreateImage(cvSize(640, 480), IPL_DEPTH_8U, 3));
       }
private:
       boost::shared_ptr<IplImage> main_image_;
}

I call updateImage in a loop. cvCreateImage dynamically allocates some memory for that image size.

The first time the loop runs, everything works ok. Now, the second time I get a _BLOCK_TYPE_IS_VALID assertion error. This happens when shared_ptr is trying to delete the pointer.

So, assuming I was doing something wrong, I tried many other options like:

if (!main_image_) 
    main_image_ = boost::shared_ptr<IplImage> (cvCreateImage...
else
    main_image_.reset(cvCreateImage...)

Didn’t work also. Tried resetting the shared_ptr first, didn’t work either. Tried setting a new temporary shared_ptr and assigning to my main_image_ ptr. No success.

Where am I going wrong here? Using regular pointers and releasing the image manually worked like a charm.

Thanks in advance,

Theo

Answer 1

I assume that you’re seeing this error in a debug build?

Which method of allocating memory does cvCreateImage() use? new or malloc()? boost::shared_ptr uses delete to destroy the memory so there might be a chance that your system detects that the data wasn’t allocated the “right way”, ie by using new.

If that’s the case then you’d have to use a shared_ptr with a custom deleter (look at the boost docs for more info) so the memory gets released correctly.