智能指针初学

Posted 2020-12-04 weiyouqing

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参考链接：https://blog.csdn.net/kang_tju/article/details/76515894

　　　　　https://www.cnblogs.com/TenosDoIt/p/3456704.html

1.auto_ptr:

#include <iostream>
#include <memory>
using namespace std;

class test
{
public:
    test(int cvalue)
    {
        m_value = cvalue;
        cout << "creat test" << m_value <<endl;
    }
    ~test()
    {
        cout << "destory test" << m_value << endl;
    }
    void setValue(int value)
    {
        m_value = value;
    }

    void getValue()
    {
        cout << m_value << endl;
    }
private:
    int m_value;
};

void testFunc(auto_ptr<test> obj)
{
    obj->getValue();
}

int main()
{
    auto_ptr<test> ptest(new test(1));
    auto_ptr<test> ptest2(new test(2));

    ptest->setValue(3);
    ptest->getValue();

    ptest2->setValue(4);
    ptest2->getValue();

    ptest = ptest2;        //将ptest2的所有权移交给了ptest.此时ptest之前的资源被析构掉了
    ptest->getValue();

    testFunc(ptest);
    //cout << ptest->getValue() << endl;    //这句话是错误的，应为auto_ptr在函数参数传递的时候，进行了一个复制。

    if (ptest2.get() == NULL)
        cout << "ptest2.get() is NULL" << endl;
    system("pause");
    return 0;
}

输出结果：

技术分享图片

2.unique_ptr:独享所有权的语义

#include <iostream>
#include <memory>
#include <vector>
using namespace std;

class test
{
public:
    test(int cvalue)
    {
        m_value = cvalue;
        cout << "creat test" << m_value <<endl;
    }
    ~test()
    {
        cout << "destory test" << m_value << endl;
    }
    void setValue(int value)
    {
        m_value = value;
    }

    void getValue()
    {
        cout << m_value << endl;
    }
private:
    int m_value;
};

void testFunc(auto_ptr<test> obj)
{
    obj->getValue();
}

void testFunc(unique_ptr<test> obj)
{
    obj->getValue();
}

int main()
{
//unique_ptr:
    unique_ptr<test> uni_test(new test(0));
    unique_ptr<test> uni_test1(new test(3));
    unique_ptr<test> tPtr;    //这里没有分配内存，因此是没有构造的；

    cout << sizeof(uni_test)<<endl;
    cout << sizeof(tPtr) << endl;

    uni_test->getValue();
    uni_test->setValue(1);
    uni_test->getValue();

    tPtr = move(uni_test);
    tPtr->setValue(2);
    tPtr->getValue();

//unique_ptr能够放在vector中
    vector<unique_ptr<test>> vec;
    vec.push_back(move(tPtr));
    vec.push_back(move(uni_test1));

    for (int i = 0 ; i < vec.size() ; i++)
    {
        vec[i]->getValue();
    }
        system("pause");
        return 0;
}

3.shaerd_ptr基于共享语义实现

#include <iostream>
#include <memory>
#include <vector>
using namespace std;

class test
{
public:
    test(int cvalue)
    {
        m_value = cvalue;
        cout << "creat test" << m_value <<endl;
    }
    ~test()
    {
        cout << "destory test" << m_value << endl;
    }
    void setValue(int value)
    {
        m_value = value;
    }

    void getValue()
    {
        cout << m_value << endl;
    }
private:
    int m_value;
};

void testFunc(auto_ptr<test> obj)
{
    obj->getValue();
}

void testFunc(unique_ptr<test> obj)
{
    obj->getValue();
}

int main()
{
    shared_ptr<test> p_test0(new test(3));
    p_test0->getValue();

    cout << "p_test0.use_count() = " << p_test0.use_count() << endl;

    shared_ptr<test> p_test1 = p_test0;

    cout << "p_test0.use_count() = " << p_test0.use_count() << endl;
    cout << "p_test1.use_count() = " << p_test1.use_count() << endl;

    shared_ptr<test> p_test2 = make_shared<test>(4);
    p_test2->getValue();

    p_test1 = p_test2;
    cout << "p_test2.use_count() = " << p_test2.use_count() << endl;
    cout << "p_test1.use_count() = " << p_test1.use_count() << endl;

    cout << "p_test0.use_count() = " << p_test0.use_count() << endl;
    system("pause");
    return  0;
}