As we saw in the previous section, circular references occur when two (or more) shared pointers reference each other in a loop, creating a deadly cycle. This interdependence prevents the destructor of the object from being called, as the reference counts never reach zero. The result is a very common memory leak which became the primary reason why weak pointers were introduced.

Breaking the cycle with weak pointers

Weak pointers are purpose-built to break these cycles. By replacing a shared pointer in a circular reference with a weak pointer, we can ensure that one of the objects does not artificially extend the lifetime of another in a manner that would prevent either from being destroyed.

To understand this concept better, let’s rewrite the linked-list circular reference problem we discussed in the previous section using a weak pointer.

In the above code, we fixed our circular reference problem by changing next from being a shared pointer to a weak pointer. Follow the comments in the above code for better understanding. And don’t forget to run the code to see the destructors being called now. No memory leaks!