c++ map 测试

// union_test.cpp : 定义控制台应用程序的入口点。
//
/*
结论：
typedef std::map<int, desktop*> deskMap; 存放的是指针，也就是到时候指针指向的内存如果改变，则结果也改变
typedef std::map<int, desktop> deskMap2; //存放的是数据，


*/

#include "stdafx.h"
#include <map>
#include <iostream>


typedef struct _desk{
    int legs;
    int id;
}desktop;

/* 注意值一个是存指针，一个是存数据 */
typedef std::map<int, desktop*> deskMap;
typedef std::map<int, desktop> deskMap2;

using namespace std;

/*结果
024
124
224
*/
void no_malloc_test()
{
    deskMap map;
    deskMap::iterator iter;
    desktop desk, *p;
    int i;


    for (i = 0; i < 3; i++)
    {
        desk.id = i;
        desk.legs = i * i;
        map.insert(deskMap::value_type(i, &desk));
    }

    for (iter = map.begin(); iter != map.end(); iter++)
    {
        p = iter->second;
        cout << iter->first << p->id << p->legs <<endl;
    }
    map.clear();
}

/*
结果:
000
111
224
*/
void no_malloc_test2()
{
    deskMap2 map;
    deskMap2::iterator iter;
    desktop desk, *p;
    int i;


    for (i = 0; i < 3; i++)
    {
        desk.id = i;
        desk.legs = i * i;
        map.insert(deskMap2::value_type(i, desk));
    }

    for (iter = map.begin(); iter != map.end(); iter++)
    {
        p = (desktop*)&iter->second;
        cout << iter->first << p->id << p->legs <<endl;
    }
    map.clear();
}


/*
结果:改变的值会保存
000
111
224
010
121
234
*/
void no_malloc_modify_test2()
{
    deskMap2 map;
    deskMap2::iterator iter;
    desktop desk, *p;
    int i;


    for (i = 0; i < 3; i++)
    {
        desk.id = i;
        desk.legs = i * i;
        map.insert(deskMap2::value_type(i, desk));
    }

    for (iter = map.begin(); iter != map.end(); iter++)
    {
        p = (desktop*)&iter->second;
        cout << iter->first << p->id << p->legs <<endl;
        p->id++;//modify
    }

        for (iter = map.begin(); iter != map.end(); iter++)
    {
        p = (desktop*)&iter->second;
        cout << iter->first << p->id << p->legs <<endl;
    }
    map.clear();
}

void new_test()
{
    deskMap map;
    deskMap::iterator iter;
    desktop *p;
    desktop *pdesk1 = new desktop;
    desktop *pdesk2 = new desktop;
    desktop *pdesk3 = new desktop;

    pdesk1->id = 0;
    pdesk1->legs = 0;

    pdesk2->id = 1;
    pdesk2->legs = 1;

    pdesk3->id = 2;
    pdesk3->legs = 4;


    map.insert(deskMap::value_type(1, pdesk1));
    map.insert(deskMap::value_type(2, pdesk2));
    map.insert(deskMap::value_type(3, pdesk3));

    /* 删除pdesk1， 输出结果如下。也就是指向同一块内存*/
    //delete pdesk1;
#if 0
1-572662307-572662307
211
324
#endif


    for (iter = map.begin(); iter != map.end(); iter++)
    {
        p = iter->second;
        cout << iter->first << p->id << p->legs <<endl;
    }
    map.clear();
}

int _tmain(int argc, _TCHAR* argv[])
{
    no_malloc_modify_test2();

    return 0;
}