30.双链表管理类的内存释放

#include <iostream>
#include <list>
#include <Windows.h>
using namespace std;

//声明类
class myclass;

struct info
{
    myclass *p;//指针,内存首地址
    int n;//代表有多少个对象
};

list<info> myclassList;//双链表数据结构管理一个类所有的对象


//类的代码区是共享的,数据是每个对象私有的
//空指针调用成员函数,没有访问数据可以调用,访问数据不可以
//重载类的new new[] delete delete[] 实现内存管理
class myclass
{
public:
    void show()
    {
        MessageBoxA(0, "hello", "hello", 0);
    }

    myclass()
    {
        cout << "myclass()" << endl;
    }

    ~myclass()
    {
        cout << "~myclass()" << endl;
    }

    void *operator new(size_t size)
    {
        cout << size << endl;
        void *p = malloc(size);
        info infonow;
        infonow.p = (myclass*)p;//分配内存就记录一下

        if(size / sizeof(myclass) == 1)
        {
            infonow.n = 1;
        }
        else
        {
            //为什么要减4因为多了一个指针的内存四个字节
            infonow.n = (size - 4) / sizeof(myclass);
        }
        myclassList.push_back(infonow);//插入链表
        return p;
    } 

    void operator delete(void *p)
    {
        //双链表中检索内存,存在就删除,不存在就不管
        for (auto ib = myclassList.begin(), ie = myclassList.end(); ib != ie; ib++)
        {
            if (p == (*ib).p)
            {
                //删除
                myclassList.erase(ib);
                free(p);
                break;
            }
        }
    }
    void *operator new[](size_t size)
    {
        cout << "new[]" << size << endl;
        return operator new(size);//回调new函数
    }
    void operator delete[](void *p)
    {
        operator delete(p);
    }
};

void showmem()
{
    //显示内存
    for (auto i : myclassList)
    {
        cout << "内存地址:" << i.p << " " << "个数:" << i.n << endl;
    }
}

void showall()
{
    for (auto i : myclassList)
    {
        if (i.n == 1)
        {
            i.p->show();
        }
        else
        {
            for (int j = 0; j < i.n; j++)
            {
                i.p[j].show();
            }
        }
    }
}

void main()
{
    myclass *p1 = new myclass;
    /*myclass *p2 = new myclass;
    myclass *p3 = new myclass;
    myclass *p4 = new myclass;*/
    myclass *p5 = new myclass[2];
    showall();
    showmem();
    cout << "-----------------" << endl;
    delete[] p5;
    delete p1;
    showmem();
    cin.get();
}