C++系列补齐 智能指针实现

#include<iostream>
#include<string>

using namespace std;

template <typename T>
class SharedPtr {
public: 
    //空参数构造,空指针
    SharedPtr() :count(0), ptr((T*)0) {}
    //构造函数count,必须new出来
    SharedPtr(T* p):count(new int(1)),ptr(p){}
    //拷贝构造函数,使其引用计数+1
    SharedPtr(SharedPtr<T>& other):count(&(++*other.count)),ptr(other.ptr){}
    T* operator->() { return ptr; }
    T& operator*() { return *ptr; }

    //重载operator =
    //如果原来的sharedptr已经有对象,则让其引用对象次数减一并判断引用是否为0
    //（是否调用delete),然后将新的引用对象次数加一
    SharedPtr<T>& operator = (SharedPtr<T>& other) {
        if (this == &other) return *this;
        ++* other.count;
        if (this->ptr && 0 == -- * this->count) {
            delete count;
            delete ptr;
            cout << "delete ptr = " << endl;
            this->ptr = other.ptr;
            this->count = other.count;
            return *this;
        }
    }
    //析构函数 使用引用次数减一并判断引用是否为零，即是否调用delete
    ~SharedPtr() {
        if (ptr && -- * count == 0) {
            delete count;
            delete ptr;
            cout << "delete ptr ~" << endl;
        }
    }
    int getRef() {
        return *count;
    }

private:
    int* count;
    T* ptr;
};



int main() {
    SharedPtr<string> pstr(new string("abc"));

    cout << "pstr:" << pstr.getRef() << " " << *pstr << endl;

    SharedPtr<string> pstr2 (pstr);
    cout << "pstr:" << pstr.getRef() << " " << *pstr << endl;
    cout << "pstr2:" << pstr2.getRef() << " " << *pstr2 << endl;

    SharedPtr<string> pstr3(new string("hao"));
    cout << "pstr3:" << pstr3.getRef() << " " << *pstr3 << endl;

    pstr3 = pstr2;
    cout << "pstr:" << pstr.getRef() << " " << *pstr << endl;
    cout << "pstr2:" << pstr2.getRef() << " " << *pstr2 << endl;
    cout << "pstr3:" << pstr3.getRef() << " " << *pstr3 << endl;

    cin.get();
    cin.get();

    return 0;
}