【Cherno的C++视频】Smart pointers in C++

#include 
#include 

// std::unique_ptr, std::shared_ptr, std::weak_ptr.
// smart pointers, when you call new, you don't have to call delete. 
// It's a wrapper around a real raw pointer, it'll call new when you make it.
//
// unique_ptr:scoped pointer, it will get destroyed if it goes out of scope. can't be copied.
// 
// shared_ptr:working by reference counting, keeps track of how many references you have to your pointer,
// as soon as that reference count reaches 0 that's when it gets deleted. can be copied.
//
// weak_ptr:assign a shared_ptr to another shared_ptr, it will increase the reference count but 
// when you assign a shared_ptr to a weak_ptr it won't increase the reference count.
//
// unique_ptr has a lower overhead, but shared_ptr is also useful in some cases, so is weak_ptr.

class Entity
{
public:
	Entity(){ std::cout << "Created Entity!" << std::endl; }

	~Entity(){ std::cout << "Destroyed Entity!" << std::endl; }

	void Function(){}
};

int main(void)
{
	{
		std::shared_ptr<Entity> e0;
		{
			//std::unique_ptr entity = std::make_unique();//more preferred way, slightly safer than std::unique_ptr uniqueEntity(new Entity());
			//entity->Function();
			std::unique_ptr another = entity;//error, can't copy a unique pointer.

			std::shared_ptr<Entity> sharedEntity = std::make_shared<Entity>();
			//std::shared_ptr sharedEntity(new Entity());//can do this too.
			//std::shared_ptr another = sharedEntity;//works.
			e0 = sharedEntity;//works.

			std::weak_ptr<Entity> weakEntity = sharedEntity;
		}
	}

	std::cin.get();
}
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