How does weak ptr work

This is especially true with thread-safe Shared Pointers, as they can become invalid at any time due to activity on another thread. The Pin function is the preferred method for any check that will lead to dereferencing or accessing the stored object, as the Shared Pointer that Pin returns will keep the object alive until your code clears it, or it goes out of scope.

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Thanks to the artificial scope in line 41 - 47, the lifetime of the mother, the son, and the daughter is limited. Or to say it the other way around.

Mother, son, and daughter go out of scope and therefore the destructor of the class Mother line 10 - 12 , Son line 25 - 27 , and Daughter line 33 - 35 should automatically be invoked. Should, because only the destructor of the class Daughter is called. The graphic or the source code shows it. Therefore, the reference counter is always greater than 0 and the destructor will not automatically be invoked. That observation holds not true for mother and daughter. This holds true for the associative and the sequential container.

Especially powerful is the automatic memory management of the sequential container std::vector and std::string. So, there are a lot of reasons for me, to have in the next post a closer look at the memory management of both containers. My special thanks to Embarcadero. I'm happy to give online seminars or face-to-face seminars worldwide. Please call me if you have any questions. Otherwise, they cannot delete their objects:. In the example above, the destructors are not called and we have a memory leak.

The managed object of a shared pointer is deleted when the reference count reaches zero. If Barca goes out of scope, it is not deleted since the managed object is still pointed by Valdes.

When Valdes goes out of scope, its managed object is not deleted either as it is pointed by Barca. The alternative would be to delete the "counter" object when both the "use count" and the "weak count" drop to zero.

Here's the first reason: Checking two pointer sized counters atomically is not possible on every platform, and even where it is, it's more complicated than checking just one counter. Another reason is that the deleter must stay valid until it has finished executing. Since the deleter is stored in the "counter" object, that means the "counter" object must stay valid. It decreases the "use count" to zero, and begins executing the deleter.

So it deletes the "counter" object, and with it the deleter. While the deleter is still running. Of course there would be different ways to assure that the "counter" object stays alive, but I think increasing the "weak count" by one is a very elegant and intuitive solution.

The "weak count" becomes the reference count for the "counter" object. Internally, to support reference-counting on an arbitrary type T, the STL or any other library implementing this kind of logic creates a wrapper object we'll call "Anchor". They do NOT update reference counts. You aren't just invoking a mutex, you're creating a strong reference from a weak one, with that "Anchor" acting.

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