You can’t do it directly, but there are a couple of ways to simulate it, with the help of the Non-Virtual Interface idiom. Use covariance on raw pointers, and then wrap them struct Base { private: virtual Base* doClone() const { … } public: shared_ptr<Base> Clone() const { return shared_ptr<Base>(doClone()); } virtual ~Base(){} }; struct … Read more
There are at least three places where you may find shared_ptr: If your C++ implementation supports C++11 (or at least the C++11 shared_ptr), then std::shared_ptr will be defined in <memory>. If your C++ implementation supports the C++ TR1 library extensions, then std::tr1::shared_ptr will likely be in <memory> (Microsoft Visual C++) or <tr1/memory> (g++’s libstdc++). Boost … Read more
This will also happen if you’ve forgotten to specify public inheritance on the derived class, i.e. if like me you write this: class Derived : Base { }; Instead of: class Derived : public Base { };
Guideline Never delete the special move members. In typical code (such as in your question), there are two motivations to delete the move members. One of those motivations produces incorrect code (as in your example), and for the other motivation the deletion of the move members is redundant (does no harm nor good). If you … Read more
Yes, it is possible to implement shared_ptr that way. Boost does and the C++11 standard also requires this behaviour. As an added flexibility shared_ptr manages more than just a reference counter. A so-called deleter is usually put into the same memory block that also contains the reference counters. But the fun part is that the … Read more
If you have circular references like this, one object should hold a weak_ptr to the other, not a shared_ptr. From the shared_ptr introduction: Because the implementation uses reference counting, cycles of shared_ptr instances will not be reclaimed. For example, if main() holds a shared_ptr to A, which directly or indirectly holds a shared_ptr back to … Read more
Firstly, this is indeed how it works in C++: the return type of a virtual function in a derived class must be the same as in the base class. There is the special exception that a function that returns a reference/pointer to some class X can be overridden by a function that returns a reference/pointer … Read more
You cannot do a global find/replace because you can copy an auto_ptr (with known consequences), but a unique_ptr can only be moved. Anything that looks like std::auto_ptr<int> p(new int); std::auto_ptr<int> p2 = p; will have to become at least like this std::unique_ptr<int> p(new int); std::unique_ptr<int> p2 = std::move(p); As for other differences, unique_ptr can handle … Read more
It will call delete[] and hence the entire array will be reclaimed but I believe you need to indicate that you are using an array form of unique_ptrby: std::unique_ptr<int[]> my_array(new int[5]); This is called as Partial Specialization of the unique_ptr.
Simple C++ Model In most modules I saw, by default, it was assumed that receiving pointers was not receiving ownership. In fact, functions/methods abandoning ownership of a pointer were both very rare and explicitly expressed that fact in their documentation. This model assumes that the user is owner only of what he/she explicitly allocates. Everything … Read more