C++智能指针实现

朴灿烈づ我的快乐病毒、 2024-04-17 15:36 62阅读 0赞

手动实现一个智能指针，留着以后用得到的时候再看

#include <iostream>
    using namespace  std;
    
    template <class T>
    class smart_ptr {
    public:
        smart_ptr (T* ptr = nullptr) : _ptr(ptr), _pCount(nullptr) {
            if (_ptr) {
                _pCount = new int (1);
            }
            cout << "smart_ptr (T* ptr)" << endl;
        }
        smart_ptr (const smart_ptr<T>& sp) : _ptr(sp._ptr), _pCount(sp._pCount){
            if (_ptr)
                (*_pCount)++;
            cout << "smart_ptr (smart_ptr<T>& ptr)" << endl;
        }
        ~smart_ptr () {
            if (_ptr && --(*_pCount) == 0) {
                delete _ptr; delete _pCount;
                _ptr = nullptr; _pCount = nullptr;
            }
            cout << "~smart_ptr ()" << endl;
        }
        smart_ptr<T>& operator= (const smart_ptr<T>& ptr) {
            cout << "smart_ptr<T> operator= (const smart_ptr<T>& ptr)" << endl;
            if (_ptr == ptr._ptr)
                return *this;
            if (_ptr && --(*_pCount) == 0) {
                delete _ptr; delete _pCount;
                _ptr = nullptr; _pCount = nullptr;
            }
            _ptr = ptr._ptr;
            _pCount = ptr._pCount;
            if (_ptr)
                ++(*_pCount);
            return *this;
        }
        int useCount () {
            return *_pCount;
        }
        T& operator* () {
            return *_ptr;
        }
        T* operator-> () {
            return _ptr;
        }
        T* get () {
            return _ptr;
        }
    
    private:
        T* _ptr;
        int* _pCount;
    };
    
    class A {
    public:
        int i;
        A (int n) : i(n) {}
        ~A () {cout << i << " destructed" << endl;}
    };
    
    int main (){
        smart_ptr<A> sp1(new A(2));
        smart_ptr<A> sp2(sp1);
        smart_ptr<A> sp3;
        sp3 = sp2;
        cout << sp1->i << "," << sp2->i << "," << sp3->i << endl;
        A* p = sp3.get();
        cout << p->i << endl;
        sp1 = new A(3);
        sp2 = new A(4);
        cout << sp1->i << endl;
        sp3 = new A(5);
        cout << "end" << endl;
        cout << (*sp3).i << " " << sp3->i << endl;
        return 0;
    }