Wrapping a releaseable object into a smart pointer

Question

As far as I understand the smart pointers, they are there to avoid memory leaks among other things. However there are often objects which also need to be released, but not by

Answer 1

Both shared_ptr and unique_ptr provide that facility.

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For shared_ptr, the constructor is a template:

An optional deleter d can be supplied that is later used to destroy the object when no shared_ptr objects own it. By default, a delete-expression for type Y is used as the deleter.

In this case, the deleter can be any callable, copy-constructible value, which get type-erased to the callable.

For unique_ptr, the type of the deleter is a type parameter of the pointer itself:

template<
    class T,
    class Deleter = std::default_delete
> class unique_ptr;

There's no erasure in this case, and the deleter provided to the c-tor or the reset actually matches the deleter type.