c - 为什么我的指针会改变固定的数字？

Question

我已经定义了自己的类型。它包含一个指向数组的指针，以及该数组中有多少项

struct neighborList
{
    unsigned int nNeighbors;
    unsigned int* pNeighbors; 
};

这些被实例化、填充，最终我想回顾它们。然后发生了一些非常奇怪的事情。我认为这里的屏幕截图比文字更好。

我已经显示了下一个要执行的语句。我有一个上述数据类型的数组，这里考虑的数组有 1 个邻居，该 1 个邻居的地址是 0x107a28；凉爽的。但实际分配给 pLook 的是什么？

地址总是偏离 0x40。有人见过这样的东西吗？感谢这里的帮助。

编辑:这就是整个内容，因为有几个人想看它。

#include "stdafx.h"
#include <stdlib.h>
#include <time.h>

//#define NVERTEX 875714
#define NVERTEX 9

struct linkedNode
{
    unsigned int node;
    linkedNode* pNextLinkedNode;
    linkedNode* pPrevLinkedNode; 
};

struct neighborList
{
    unsigned int nNeighbors;
    unsigned int* pNeighbors; 
};

struct linkedNodeList
{
    linkedNode* pHead;
    linkedNode* pTail;
};

void populateNeighbors(neighborList* pNeighborList, FILE* fp);
void DFSLoop(neighborList* pNeighborList, linkedNode* pOutput, unsigned int nNodes); 
void append(linkedNodeList* pLinkedList, unsigned int node);

void DFSLoop(neighborList* pNeighborList, linkedNodeList* pOutput, unsigned int nNodes)
{
    bool* visitedArray;
    bool* cashedArray;
    unsigned int* leaderArray;
    unsigned int* finishingTimes;
    unsigned int t = 0; 

    visitedArray = (bool*)malloc(nNodes*sizeof(bool));
    cashedArray = (bool*)malloc(nNodes*sizeof(bool)); 
    leaderArray = (unsigned int*)malloc(nNodes*sizeof(unsigned int)); 
    finishingTimes = (unsigned int*)malloc(nNodes*sizeof(unsigned int)); 

    //initialize all arrays to all false/0
    for (unsigned int i = 0; i < nNodes; i++)
    {
        visitedArray[i] = false;
        cashedArray[i] = false; 
        leaderArray[i] = 0;
        finishingTimes[i] = 0;
    }

    //firstly, pick a starting node and put it on the linkedList
    //initialize head and tail
    (pOutput->pHead)->node = 1;
    (pOutput->pHead)->pNextLinkedNode = NULL;
    (pOutput->pHead)->pPrevLinkedNode = NULL;

    (pOutput->pTail)->node = 1;
    (pOutput->pTail)->pNextLinkedNode = NULL;
    (pOutput->pTail)->pPrevLinkedNode = NULL;

    unsigned int curNode = (pOutput->pTail)->node;
    for (;;)
    {
        //Start DFS
        //#1 If current node under consideration has an unexplored neighbor, make it the new tail and repeat
        //   If not, current node is cashed. Set it's finishing time, and leader. Work back through the list
        //   Until you find a node with an unexplored neighbor
        unsigned int nNeighbors = pNeighborList[curNode].nNeighbors;

        for (unsigned int i = 0; i < nNeighbors; i++)
        {
            unsigned int* pLook = (pNeighborList[curNode]).pNeighbors;
            unsigned int neighbor = pLook[0];
            /*
            unsigned int nodeUnderConsideration = (pNeighborList[curNode].pNeighbors)[i];

            if ( !cashedArray[nodeUnderConsideration])
            {
                append(pOutput, (pNeighborList[curNode].pNeighbors)[i]); 
                curNode = (pOutput->pTail)->node;
                continue; 
            }
            */
        }


        //#2 If you make it back to the head and have no unexplored neighbors, pick new vertex (if unvisited) and repeat



    }


    free(visitedArray);
    free(cashedArray); 
    free(leaderArray);
    free(finishingTimes); 
}

int _tmain(int argc, _TCHAR* argv[])
{
    //open file
    FILE* fp;
    FILE* fpRev;
    //fp = fopen("SCC.txt", "rb"); 
    //fpRev = fopen("SSCrev.txt", "rb"); 
    fp = fopen("SSCsmall1.txt", "rb"); 
    fpRev = fopen("SSCsmall1rev.txt", "rb");

    /* read file. When reading, keep track of how much memory to malloc */
    /* for each vertex */
    neighborList* pAllEdges;
    neighborList* pAllEdgesRev;
    pAllEdges = (neighborList*)malloc(NVERTEX*sizeof(neighborList)); 
    pAllEdgesRev = (neighborList*)malloc(NVERTEX*sizeof(neighborList)); 

    populateNeighbors(pAllEdges, fp);
    populateNeighbors(pAllEdgesRev, fpRev); 

    //instantiate pointers for linkedlists needed for DFS
    linkedNodeList NodesFirstPass, NodesSecondPass;
    NodesFirstPass.pHead = (linkedNode*)malloc(sizeof(linkedNode)); 
    NodesFirstPass.pTail = NodesFirstPass.pHead; 
    NodesSecondPass.pHead = (linkedNode*)malloc(sizeof(linkedNode)); 
    NodesSecondPass.pTail = NodesSecondPass.pHead; 

    DFSLoop(pAllEdges, &NodesFirstPass, NVERTEX); 

    free(pAllEdges); 
    free(pAllEdgesRev); 
    return 0;
}

void populateNeighbors(neighborList* pNeighborList, FILE* fp)
{
    unsigned int v1 = 1;
    unsigned int v2 = 1;

    unsigned int v1_next = 1;
    unsigned int v2_next = 1; 
    unsigned int neighbors [1000]; 
    fscanf(fp, "%u", &v1_next); 
    fscanf(fp, "%u", &v2_next); 

    for (unsigned int i = 0; i < (NVERTEX - 1); i++)
    {
        //initialize nNeigbors to 0
        unsigned int nNeighbors = 0;

        for (;;)
        {
            //if v1_next is a different vertex then v1, then copy v1_next to v1, 
            //malloc what we need to, copy over the array and continue
            if (v1_next != v1)
            {
                pNeighborList[i].nNeighbors = nNeighbors; 

                if (nNeighbors != 0) 
                {
                    pNeighborList[i].pNeighbors = (unsigned int*)malloc(nNeighbors * sizeof(unsigned int));

                    for (unsigned int j = 0; j < nNeighbors; j++)
                    {
                        pNeighborList[i].pNeighbors[j] = neighbors[j]; 
                    }

                }

                v1++;
                break;
            }

            //else, increment the neighbor count for this particular vertex and continue
            //within this loop, getting new neighbors (edges)
            else
            {
                neighbors[nNeighbors] = v2_next; 
                nNeighbors++;
                if (nNeighbors == 1000) 
                {
                    break; 
                }
                fscanf(fp, "%u", &v1_next);
                fscanf(fp, "%u", &v2_next); 
            }
        }
    }

}

void append(linkedNodeList* pLinkedList, unsigned int node)
{
    //make new node with the intention that it's going to be the new tail
    linkedNode* pNewNode = (linkedNode*)malloc(sizeof(linkedNode));
    pNewNode->node = node; 
    pNewNode->pNextLinkedNode = NULL;
    pNewNode->pPrevLinkedNode = pLinkedList->pTail;

    //set next node of current tail to new node
    (pLinkedList->pTail)->pNextLinkedNode = pNewNode; 

    //new tail becomes new node
    pLinkedList->pTail = pNewNode; 

    //lastly, set old tail's next node to point to new tail
    (pLinkedList->pTail->pPrevLinkedNode)->pNextLinkedNode = pLinkedList->pTail;
}

Answer 1

从屏幕截图来看，假设您使用的是 64 位系统(指针有 8 个字节宽)，指针 pNeighborList 链接到列表的开始 ，而 pLook 链接到 索引 5 处 neighborList 元素的 pNeighbors 属性:

// assuming sizeof(neighborList) == 4 (int) + 8 (pointer) = 12 bytes

neighborList* pNeighborList = new neighborList[10];
// pNeighborList points to the start of the list, 0x00107a28

// pNeighborList[5] is at address 0x00107a64 (start + 5 * sizeof(neighborList)
// .pNeighbors is offset 4 more bytes (sizeof(unsigned int)) = 0x00107a68

int curNode = 5;
unsigned int* pLook = (pNeighborList[curNode]).pNeighbors;
// pLook points to pNeighbors of the element at index 5, 0x00107a68

当您将指针悬停在 Visual Studio 中的 pNeighborList 时，它会显示指针(指向列表的开头)，而不是完整值 ((pNeighborList[curNode]) .pNeighbors)。