【C/C++】如何利用char型数组buffer存放指针

由于内存规划限制，某数据结构中不能再增加新的指针，但该结构的char数组型buffer中存在一些可用空间。

于是使用了如下方法保存回调函数指针和链表结构。

先把代码放上来，有时间再补充文字介绍。

#include <iostream>
#include <string>
#include <list>
#include <fstream>
using namespace std;

#define ADD 1
#define SUB 2
#define CALLBACK_PTR_POS 46
#define PREV_PTR_POS 4
#define NEXT_PTR_POS 17

struct Obj
{
    int para1;
    int para2;
    char buf[64];
};


int Add(int para1, int para2)
{
   int ret = para1 + para2;
   cout << para1 << " + " << para2 << " = " << ret << endl;
   return ret;
}

int Sub(int para1, int para2)
{
    int ret = para1 - para2;
    cout << para1 << " - " << para2 << " = " << ret << endl;
    return ret;
}


Obj* CreateObj(int para1, int para2, int type)
{
    Obj* pObj = new Obj;
    pObj->para1 = para1;
    pObj->para2 = para2;
    switch(type)
    {
    case ADD:
        *(int(**)(int,int))(&(pObj->buf[CALLBACK_PTR_POS])) = Add;
        break;
    case SUB:
        *(int(**)(int,int))(&(pObj->buf[CALLBACK_PTR_POS])) = Sub;
        break;
    default:
        return NULL;
    }
    return pObj;
}

int DestroyObj(Obj* pObj)
{
    if (NULL == pObj)
        return -1;

    delete pObj;
    return 0;
}

void OperateObj(Obj* pObj)
{
    (*(int(**)(int,int))(&(pObj->buf[CALLBACK_PTR_POS])))(pObj->para1, pObj->para2);
}


inline void RegistNeighbor(Obj* front, Obj* back)
{
    if (NULL != front)
        *(Obj**)(&front->buf[NEXT_PTR_POS]) = back;

    if (NULL != back)
        *(Obj**)(&back->buf[PREV_PTR_POS]) = front;
}

Obj* startPos = NULL;;

int Init(const string& fileName)
{
    ifstream ifs(fileName.c_str());
    int para1, para2, op;
    Obj* prev = NULL;
    Obj* cur = NULL;

    while (ifs >> para1 >> para2 >> op && NULL == (cur = CreateObj(para1, para2, op)))
    {
        /*intentionally left blank*/
    }

    startPos = cur;
    RegistNeighbor(NULL, cur);
    prev = cur;

    while (ifs >> para1 >> para2 >> op)
    {
        cur = CreateObj(para1, para2, op);
        if (NULL == cur)
            continue;
        RegistNeighbor(prev, cur);
        prev = cur;
    }
    RegistNeighbor(cur, NULL);
    return 0;
}


int Work()
{
    Obj* curObj = startPos;
    while (NULL != curObj)
    {
        OperateObj(curObj);
        Obj* prevObj = curObj;
        curObj = *(Obj**)(&prevObj->buf[NEXT_PTR_POS]);
        DestroyObj(prevObj);
    }
    return 0;
}


int main(int argc, char** argv)
{
    Init(argv[1]);

    Work();
}