[英]Why does my pointer change by a fixed number?
我已經定義了自己的類型。 它包含一個指向數組的指針,以及該數組中有多少項
struct neighborList
{
unsigned int nNeighbors;
unsigned int* pNeighbors;
};
這些實例化,填充,最后我想回顧它們。 然后發生非常奇怪的事情。 我認為屏幕截圖比這里的文字更好。
我已經顯示了要執行的下一條語句。 我有一個上述數據類型的數組,這里考慮的一個有1個鄰居,那個1個鄰居的地址是0x107a28; 涼。 但是實際上分配給pLook的是什么?
地址始終關閉0x40。 有人看到過這樣的東西嗎? 感謝您的幫助。
編輯:這是整個過程,因為有幾個人希望看到它。
#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;
}
從屏幕快照來看,並假設您使用的是64位系統(指針為8字節寬),指針pNeighborList
鏈接到列表的開頭 ,而pLook
鏈接到索引5的neighborList
元素的pNeighbors
屬性:
// 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
當您將指針pNeighborList
在Visual Studio中的指針pNeighborList
時,它將顯示指針(指向列表的開頭),而不是完整值( (pNeighborList[curNode]).pNeighbors
)。
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