Effective C++规定45 附加代码

这部分是额外的代码的博客。键45条款想法已经实现。

#include<iostream>
using namespace std;

template<typename T>
class SharedPtr
{
public:
    template<typename U>
    SharedPtr(const SharedPtr<U>&u) :ptr(u.get())
    {
        count++;
    }
    SharedPtr(T*ptr_):ptr(ptr_){}
    T*get()const{ return ptr; }
    ~SharedPtr()
    {
        if (1 == count)
        {
            count--;
            delete ptr;
            ptr = NULL;
        }
    }
private:
    T* ptr;
    int count;

};

class A{};
class B :public A{};
class C{};

int main()
{
    SharedPtr<B> b1(new B());
    SharedPtr<C> c1(new C());
    SharedPtr<A> a1 = b1;
    SharedPtr<A> a2 = c;//不能通过编译

    return 0; 

}