问题
I need to use a shared_ptr here because I can't change the API.
Foo1 *foo1 = new Foo1(...);
shared_ptr<Foo2> foo2(foo1);
Is the shared_ptr here going to handle freeing the memory used by foo1? If I understand correctly, I shouldn't have to call delete on foo1 correct?
回答1:
Yes. You are correct, but the correct way to initialise foo2 is:
std::shared_ptr<Foo2> foo2 = std::make_shared<Foo1>();
Herb Sutter discusses the reasons why you should use std::make_shared<>() here:
https://herbsutter.com/2013/05/29/gotw-89-solution-smart-pointers/
回答2:
You shouldn't call delete on foo1.
Better you shouldn't create foo1. Only foo2:
shared_ptr<Foo2> foo2(new Foo1(...));
- std::shared_ptr: http://en.cppreference.com/w/cpp/memory/shared_ptr
std::shared_ptr is a smart pointer that retains shared ownership of an object through a pointer.
If you do not need this pointer to be shared - consider to use std::unique_ptr
- std::unique_ptr: http://en.cppreference.com/w/cpp/memory/unique_ptr
std::unique_ptr is a smart pointer that: retains sole ownership of an object through a pointer, and destroys the pointed-to object when the unique_ptr goes out of scope.
回答3:
Correct. The smart pointers provide ownership semantics. In particular, the semantics provided by std::shared_ptr are such that the object will be deleted once the last shared_ptr pointing to it is destroyed. shared_ptr keeps a reference count (how many shared_ptrs are referring to the object) and when it reaches 0, it deletes the object.
来源：https://stackoverflow.com/questions/12713004/will-a-shared-ptr-automatically-free-up-memory