面试时实现智能指针shared_ptr

转载:面试时实现智能指针

#include<iostream>
#include<cstdio>
using namespace std;
template<typename T>
class SmartPointer
{
public:
	//构造函数
	SmartPointer(T* ptr)
	{
		ref = ptr;
		ref_count = (unsigned int*)malloc(sizeof(unsigned));
		*ref_count = 1;
	}
	//拷贝构造函数
	SmartPointer(const SmartPointer<T>& other)
	{
		ref = other.ref;
		ref_count = other.ref_count;
		++*ref_count;//引用计数增加
	}
	//赋值运算符重载
	SmartPointer& operator=(SmartPointer<T>& other)
	{
		if (this == &other)
			return *this;
		//引用计数为0时调用析构
		if (--*ref_count == 0)
		{
			clear();
		}
		ref = other.ref;
		ref_count = other.ref_count;
		++*ref_count;

		return *this;
	}
	//取地址
	T& operator*()
	{
		return *ref;
	}
	//取值
	T* operator->()
	{
		return ref;
	}
	//析构函数
	~SmartPointer()
	{
		if (--*ref_count == 0)
		{
			clear();
		}

	}
private:
	//析构处理
	void clear()
	{
		delete ref;
		free(ref_count);
		ref = NULL;
		ref_count = NULL;
	}
protected:
	T* ref;//指针
	unsigned int* ref_count;//引用计数
};

void main()
{

	int* p = new int();
	*p = 11;
	SmartPointer<int> ptr1(p);
	SmartPointer<int> ptr2 = ptr1;
	*ptr1 = 1;
	cout << *ptr1 << " " << *ptr2 << endl;
}