目录

1. 几种智能指针

1.1 shared_ptr

1. 几种智能指针

[code]1. auto_ptr: c++11中推荐不使用他

2. shared_ptr: 每添加一次引用 就+1，减少一次引用，就-1；做到指针进行共享

3. unique_ptr: 一个指针同时只能有一个使用者使用

4. weaked_ptr: 与shared_ptr搭配使用

1.1 shared_ptr

参考：https://zh.cppreference.com/w/cpp/memory/shared_ptr

std::shared_ptr

shared_ptr

• 最后剩下的占有对象的 

  shared_ptr

   被销毁；
• 最后剩下的占有对象的 

  shared_ptr

   被通过 operator= 或 reset() 赋值为另一指针。

[code]#include <iostream>
#include <memory>
#include <thread>
#include <chrono>
#include <mutex>

class Object
{
public:
Object(int id) : m_id(id) {
std::cout << "init obj " << m_id << std::endl;
}
~Object() {
std::cout << "bye bye " << m_id << std::endl;
}
int id() const {
return m_id;
}
private:
int m_id;
};

typedef std::shared_ptr<Object> ObjectPtr;

void print(ObjectPtr obj);
void printRef(const ObjectPtr& obj);

void interfaceOfSharedPtr()
{
ObjectPtr null;
std::cout << "ref count is " << null.use_count() << std::endl; // 0

ObjectPtr obj(new Object(1));
std::cout << "ref count is " << obj.use_count() << std::endl;  // 1

ObjectPtr obj2(obj);
std::cout << "ref count is " << obj.use_count() << std::endl;  // 2

ObjectPtr obj3 = obj;
std::cout << "ref count is " << obj.use_count() << std::endl;  // 3

obj2.reset();        // 不需要了
//obj2 = nullptr;    // c++11写法
std::cout << "ref count is " << obj.use_count() << std::endl;  // 2

ObjectPtr obj4;
obj3.swap(obj4);
//std::swap(obj3, obj4);   // 本身管理资源，引用数没有变化
std::cout << "ref count is " << obj.use_count() << std::endl;  // 2

auto p = obj.get();
if (p)
{
std::cout << "id is " << p->id() << std::endl;
}

if (obj)
{
std::cout << "p id is " << obj->id() << std::endl;        // operator ->
std::cout << "ref id is " << (*obj).id() << std::endl;    // operator *
}

obj4 = nullptr;
//   if (obj.unique())          //效率更高
//   if (obj.use_count() == 1)  // 会有效率损失

std::cout << "only one hold ptr " << obj.unique() << std::endl;
// 值传入
print(obj);
std::cout << "ref count is " << obj.use_count() << std::endl;

// 引用传入, 推荐
printRef(obj);
}

void print(ObjectPtr obj)         // 值传入，会临时改变引用数量+1
{
std::cout << "count " << obj.use_count() << " id " << obj->id()
<< std::endl;       // 3
}

void printRef(const ObjectPtr& obj)  // 引用传递不会改变引用数量
{
std::cout << "ref count " << obj.use_count() << " id " << obj->id()
<< std::endl;       // 2
}

void deleteOfObject(Object* obj)
{
if (obj) {
std::cout << "delete obj " << obj->id() << std::endl;
delete obj;
}
}

void useDeleter()
{
// 管理 裸指针 和 处理这个指针的函数 -- 可以管理应用delete资源，也可以管理其他类似资源
ObjectPtr obj(new Object(2), deleteOfObject);
ObjectPtr obj2 = obj;
}

int main()
{

interfaceOfSharedPtr();

return 0;
}

[code]ref count is 0
init obj 1
ref count is 1
ref count is 2
ref count is 3
ref count is 2
ref count is 2
id is 1
p id is 1
ref id is 1
only one hold ptr 1
count 2 id 1
ref count is 1
ref count 1 id 1
bye bye 1