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POSmart pointers with a library written in C
 

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    <p>I'm using C++ with the OpenCV library, which is a library image-processing although that's not relevant for this question. Currently I have a design decision to make. </p> <p>OpenCV, being a C library, has its data structures (such as CvMat) declared as structs. To create them, you use functions like cvCreateMat, and to release them, you use functions like cvReleaseMat. Being a C++ programmer, I created a special <code>cv_scoped</code> class which would automatically call cvReleaseMat when it went out of scope (like <code>boost::scoped_ptr</code>). </p> <p>What I'm realising now is that I wish I could use <code>auto_ptr</code> and <code>shared_ptr</code> in cases as well. I just feel that writing code for my own <code>cv_auto_ptr</code> and <code>cv_shared_ptr</code> classes would be a bad idea, not to mention a waste of time. So I've been looking for solutions, and I've come up with three possibilities.</p> <p><strong>First</strong>, I could use the cv_scoped class I've already made. I'd rename it to <code>cv_ptr</code> and then use smart pointers like so: <code>std::auto_ptr&lt;cv_ptr&gt;</code>. The annoying thing about this though is, I'd always have to dereference twice:</p> <pre><code>std::auto_ptr&lt;cv_ptr&gt; matrix(cv_ptr(cvCreateMat(320, 240, CV_32FC3))); cvPow(matrix.get()-&gt;get()); // one get for the auto_ptr, one for the cv_ptr </code></pre> <p>I know it looks like I could declare an implicit conversion, but I couldn't actually - most of OpenCV's functions have the parameter void* - so no implicit conversion would be called. I would really like a way of doing this where I didn't have to do the double dereference.</p> <p><strong>Second</strong>, I could somehow override <code>operator delete</code>. I don't want to override the global operator delete because I'd only want this to apply to CvMat (and a few other) types. However, I can't change the library, so I can't add <code>operator delete</code> to the CvMat struct. So I don't know how this would work.</p> <p><strong>Third</strong>, I could just rewrite my own <code>auto_ptr</code>, <code>scoped_ptr</code>, and <code>shared_ptr</code>. They're not large classes so it wouldn't be too difficult, but I just feel like this is bad design. If I were to do this, I would probably do something along these lines:</p> <pre><code>class cv_auto_ptr { public: cv_auto_ptr(); ~cv_auto_ptr(); // each method would just be a proxy for the smart pointer CvMat* get() { return this-&gt;matrix_.get()-&gt;get(); } // all the other operators/methods in auto_ptr would be the same, you get the idea private: auto_ptr&lt;cv_ptr&gt; matrix_; // cv_ptr deletes CvMat properly } </code></pre> <p>What would you do in my situation? Please help me figure this one out.</p>
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