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

You can construct both shared_ptr (signature #3 here) and unique_ptr (signature #2 here) with custom deleters.

using T = ...;
auto deleter = [](T* x) { delete x; };

// different deleter - different unique_ptr type
// deleter is stored inline
auto x = std::unique_ptr(new T(...), deleter);

// same shared_ptr type regardless of the deleter type,
// deleter is stored in the "shared state"
auto y = std::shared_ptr(new T(...), deleter);

Note, make_shared() cannot be used to construct a shared_ptr with custom deleter.