C++智能指针实现-蒲公英云

C++智能指针实现

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;
}