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Deep copy of list of instances with cv::Mat members

asked 2013-07-17 18:49:43 -0500

B. Bogart gravatar image

What is the best way to make a deep copy of a list of instances who have Mat members?

Lets say I have this class:

class myClass {
    public:
        Mat image;

        myClass(Scalar value) {
            this->image =  Mat(300, 300, CV_8UC3, value);
        }
};

I can populate a list of instances with:

instances.push_back(myClass(Scalar(0,255,0)));
instances.push_back(myClass(Scalar(0,255,255)));

Now I would like a second list that is a deep copy of the instances including the underlying Mat data. Just doing the following does a shallow copy:

list<myClass> newInstances = instances;

The problem is that I have opencv doing some vision stuff in one thread, and I want to copy the data into the main renderer such that the renderer will not keep data from being cleared in the thread.

Thanks.

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answered 2013-07-17 19:17:51 -0500

berak gravatar image

a simple

Mat a, b; 
a = b;

assignment will only copy the Mat structure, and assign b's pixel pointer to a

for a "deep copy" ( esp. of the pixels ), i think, you want

a = b.clone()

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Ok, but how do I make the assignment operator for the list of instances do clone rather than assignment? I could just make a loop and manually copy, but I'm doing these operations in a lot of different places and overriding assignment for these instances would be better.

B. Bogart gravatar imageB. Bogart ( 2013-07-18 11:31:36 -0500 )edit

understandable request ;)

let me play a bit with it ..

berak gravatar imageberak ( 2013-07-18 11:53:18 -0500 )edit

nice puzzle, how far did you come there ?

could not find something real satisfying.

http://bpaste.net/show/QhIHCVrR7hq9FwsBBQpF/

berak gravatar imageberak ( 2013-07-18 13:22:07 -0500 )edit

I did not consider that overriding the assignment operator would probably cause a lot of other unintended consequences when passing around my classes. Seems a custom function that does a manual deep copy is the best way to go.

B. Bogart gravatar imageB. Bogart ( 2013-07-19 12:52:00 -0500 )edit

yes, think so, too.

berak gravatar imageberak ( 2013-07-19 12:59:08 -0500 )edit

@berak, I was about to ask this question again, to find I already had! I'm trying to replace an instance containing a mat with a new instance (or a copy of all the members), but my replacement causes a leak. using clone() does not solve the leak. Please see this post: http://stackoverflow.com/questions/18772065/how-to-replace-an-instance-with-another-instance-via-pointer

B. Bogart gravatar imageB. Bogart ( 2013-09-13 16:03:27 -0500 )edit
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Asked: 2013-07-17 18:49:43 -0500

Seen: 818 times

Last updated: Jul 17 '13