CODEWITHSUNDEEP
c++classmemorystdshared-ptr
nick huang
nick huang

Reputation: 463

Should I always use shared_ptr to create a class instance(instead of just new)?

As wiki shows, shared_ptr can handle the heap space recycle problems. So, I always use shared_ptr to create instance, is there any problems?

and I use it as this, i dont need to delete s, right?

s = std::shared_ptr<S>(new S).get();

Upvotes: 1

Views: 2521

Answers (1)

Fibbs
Fibbs

Reputation: 1420

You shouldn't always use shared_ptr because there are more types of smart pointer than just shared_ptr. The Standard Library also provides unique_ptr for example. You must evaluate which better suits the task at hand.

Smart pointers in general are however the preferred way of safely handling dynamically allocated objects in modern C++. As a general rule of thumb, avoid the use of new and delete unless you encounter a problem that can't be solved without them.

As an aside, your example will not work as you expect.

auto s = std::shared_ptr(new S).get();

This will create a dangling pointer. The call to new dynamically allocates an object of type S. A pointer to it is given to the constructor for shared_ptr which now manages the object lifetime. You then assign a copy of the raw pointer of S to s via get(). At the end of the line the shared_ptr destructor frees S meaning that whatever s points to is undefined.

The correct way to create a shared pointer would be:

auto s = std::make_shared<S>();

Upvotes: 3

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