当我运行以下代码时出现分段错误/故障

Question

我是C语言的新手。当我在在线C编译器中运行下面的图遍历算法程序时出现分段错误。我知道错误是由于访问了未初始化或无法访问的内存，但我不知道错误发生在哪里。

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#define max 5
struct vertex{
    char name;
    bool isVisited;
};
int queue[max];
int rear = -1, front = 0, queueCount = 0, vertexCount = 0;
struct vertex* adjList[max];
int adjMat[max][max];
void insert(int data){
    queue[++rear] = data;
    queueCount++;
}
int delete(){
    queueCount--;
    return queue[front++];
}
bool isEmpty(){
    return queueCount == 0;
}
void addVertex(char name){
    struct vertex* v = (struct vertex*)malloc(sizeof(struct vertex));
    v->name = name;
    v->isVisited = false;
    adjList[vertexCount++] = v;
}
void addEdge(int start, int end){
    adjMat[end][start] = 1;
    adjMat[start][end] = 1;
}
void display(int vertexIndex){
    printf("%c", adjList[vertexIndex]->name);
}
int getAdjUnvisitedVertices(int vertexIndex){
    for (int i = 0; i < vertexCount; i++){
        if (adjMat[vertexIndex][i] == 1 && adjList[i]->isVisited == false){
            return i;
        }
    }
    return -1;
}
void BFS(){
    adjList[0]->isVisited = true;
    display(0);
    insert(0);
    int unvisitedVertex;
    while (!isEmpty()){
        int tempVertex = delete();
        while (unvisitedVertex = getAdjUnvisitedVertices(tempVertex) != -1){
            adjList[unvisitedVertex]->isVisited = true;
            display(unvisitedVertex);
            insert(unvisitedVertex);
        }
    }
    for (int i = 0; i < vertexCount; i++){
        adjList[i]->isVisited = false;
    }
}
void main(){
    for (int i = 0; i < max; i++){
        for (int j = 0; j < max; j++){
            adjMat[i][j] = 0;
        }
    }
    addVertex('S');
    addVertex('A');
    addVertex('B');
    addVertex('C');
    addVertex('D');
    addEdge(0,1);
    addEdge(0,2);
    addEdge(0,3);
    addEdge(1,4);
    addEdge(2,4);
    addEdge(3,4);
    printf("Breadth First Traversal : ");
    BFS();
}

Answer 1

使用 gcc -g -fsanitize=address a.c && ./a.out 结果：

=================================================================
==2590725==ERROR: AddressSanitizer: global-buffer-overflow on address 0x563fc7b38394 at pc 0x563fc7b35262 bp 0x7ffe7e7fd600 sp 0x7ffe7e7fd5f8
WRITE of size 4 at 0x563fc7b38394 thread T0
    #0 0x563fc7b35261 in insert /tmp/a.c:14
    #1 0x563fc7b35839 in BFS /tmp/a.c:55
    #2 0x563fc7b35a89 in main /tmp/a.c:80
    #3 0x7fe91f032e49 in __libc_start_main ../csu/libc-start.c:314
    #4 0x563fc7b35139 in _start (/tmp/a.out+0x1139)

0x563fc7b38394 is located 0 bytes to the right of global variable 'queue' defined in 'a.c:9:5' (0x563fc7b38380) of size 20
0x563fc7b38394 is located 44 bytes to the left of global variable 'front' defined in 'a.c:10:16' (0x563fc7b383c0) of size 4

第 14 行是：

     queue[++rear] = data;

所以在问题点，rear索引超过5。

Answer 2

此处出现无限循环导致数组边界异常。原因是赋值语句没有执行。

 while (unvisitedVertex = getAdjUnvisitedVertices(tempVertex) != -1)

为确保赋值操作与条件运算符一起发生，需要用括号括起来。

while ((unvisitedVertex = getAdjUnvisitedVertices(tempVertex)) != -1)

这个变化的结果是广度优先遍历： SABCD

当我运行以下代码时出现分段错误/故障

I am getting segmentation error /fault when I run the below code

c

memory

runtime-error

graph

segmentation-fault

当我 运行 以下代码时出现分段错误/故障

I am getting segmentation error /fault when I run the below code

c

memory

runtime-error

graph

segmentation-fault

当我运行以下代码时出现分段错误/故障