一个shared_ptr的简易实现

#include<iostream>


class SharedCount{
public:
	SharedCount():count_(1){}
	void AddCount(){
		++count_;
	}
	long ReduceCount(){
		return --count_;
	}
	long GetCount() const{
		return count_;
	}

	template<typename T>
	friend class SharedPtr;

private:
	long count_;
};


template<typename T>
class SharedPtr{
public:
	explicit SharedPtr(T *ptr=nullptr):ptr_(ptr){
		if(ptr_){
			rel_ = new SharedCount();
		}else{
			rel_ = nullptr;
		}
	};

	~SharedPtr(){
		if(rel_ && !rel_->ReduceCount()){
			delete ptr_;
			delete rel_;
		}
	}

	SharedPtr(const SharedPtr& other){
		rel_ = other.rel_;
		if(rel_){
			rel_->AddCount();
		}
		ptr_ = other.ptr_;
	}


	SharedPtr(SharedPtr&& other){
		ptr_ = other.ptr_;
		rel_ = other.rel_;

		other.ptr_ = nullptr;
		other.res_ = nullptr;
	}

	SharedPtr& operator=(SharedPtr& rhs){
		if(ptr_ != rhs.ptr_){
			if(rel_ && !rel_->ReduceCount()){
				delete ptr_;
				delete rel_;
			}
			rhs.rel_->AddCount();
			ptr_ = rhs.ptr_;
			rel_ = rhs.rel_;
		}

		return *this;
	}

	T* Get() const{
		return ptr_;
	}

	long UseCount() const{
		if(ptr_){
			return rel_->GetCount();
		}else{
			return 0;
		}
	}


	T& operator*() const{
		return *ptr_;
	}
	T* operator->() const{
		return ptr_;
	}
	operator bool() const{
		return ptr_;
	}


private:
	T *ptr_;
	SharedCount *rel_;
};


int main(){
	SharedPtr<int> sp1(new int(5));
	SharedPtr<int> sp2;
	std::cout << "sp1.use_count:  " << sp1.UseCount() << std::endl;
	std::cout << "sp2.use_count:  " << sp2.UseCount() << std::endl;

	sp2 = sp1;
	std::cout << "sp1.use_count:  " << sp1.UseCount() << std::endl;
	std::cout << "sp2.use_count:  " << sp2.UseCount() << std::endl;

	SharedPtr<int> sp3(sp2);
	std::cout << "sp1.use_count:  " << sp1.UseCount() << std::endl;
	std::cout << "sp2.use_count:  " << sp2.UseCount() << std::endl;
	std::cout << "sp3.use_count:  " << sp3.UseCount() << std::endl;

	return 0;
}