c++ - Ubuntu 机器上的段错误，但 Mac 上没有

Question

我在 Mac 机器上做作业，代码编译后我得到了预期的输出。一旦我去运行程序进行评分的 Ubuntu 机器上对其进行测试，我就会收到段错误(核心转储)错误消息。我真的很困惑，正在寻找一些技巧来调试为什么在 ubuntu 机器(版本 12.04)而不是 mac 机器(mavericks OS)上发生这种情况。

编辑:通过 gdb 运行它，我在

得到了段错误

in getPath: line 28, if (path[position] == 0 && position == 0) {

我的代码如下:

#include <iostream>

using namespace std;

int minDistance(int distance[], bool shortestPath[]) {

    int min = 1000000000;
    int indexOfMin;

    for (int i = 0; i < 6; i++) {
        if (shortestPath[i] == false && distance[i] <= min) {
            min = distance[i]; 
            indexOfMin = i;
        }
    }

    return indexOfMin;
}

void getPath(int path[], int position) {
    cout << position + 1 << " <- ";

    // base case, we hit the end of the path
    if (path[position] == 0 && position == 0) {
        cout << path[position] + 1 << endl;
    }
    else if (path[position] == 0)
        cout << path[position] + 1 << endl;
    else {
        getPath(path, path[position]);
    }
}

void dijkstraAlgorithm(int weightedGraph[6][6], int sourceVertex) {
    int distance[6];     
    bool shortestPath[6]; 
    int path[6]; 

    for (int i = 0; i < 6; i++) {
        distance[i] = 1000000000; 
        shortestPath[i] = false;
    }

    distance[sourceVertex] = 0;

    for (int j = 0; j < 5; j++) {
        int min = minDistance(distance, shortestPath);
        shortestPath[min] = true;
        for (int k = 0; k < 6; k++) {
            if (!shortestPath[k] && weightedGraph[min][k] && distance[min] != 1000000000 && distance[min] + weightedGraph[min][k] < distance[k]) {
                distance[k] = weightedGraph[min][k] + distance[min];
                path[k] = min;
            }
        }
    }

    cout << "Distance       Path" << endl;
    for (int i = 0; i < 6; i++) {
        // dist[i] == 0 a formatting fix for first distance
        if (distance[i] == 0) {
            cout << distance[i] << ":            ";
            getPath(path, i);
        }
        else {
            cout << distance[i] << ":           ";
            getPath(path, i);
        }
    }
}

int main() {
    int weightedGraph[6][6] = {
        {0, 10, 0, 30, 100, 0},
        {0, 0, 50, 0, 0, 0},
        {0, 0, 0, 0, 10, 5},
        {0, 0, 20, 0, 0, 15},
        {0, 0, 0, 60, 0, 0},
        {0, 0, 0, 0, 0, 0}
    };

    dijkstraAlgorithm(weightedGraph, 0);

    return 0;
}

注意:我需要在Ubuntu环境下使用g++编译器(版本4.6.4)

Answer 1

在 valgrind 下运行您的示例代码显示这些 uninitialized read错误:

==25442== Conditional jump or move depends on uninitialised value(s)
==25442==    at 0x4008B2: getPath(int*, int) (crash.cpp:24)
==25442==    by 0x400B19: dijkstraAlgorithm(int (*) [6], int) (crash.cpp:62)
==25442==    by 0x400B9C: main (crash.cpp:81)

和:

==25442== Conditional jump or move depends on uninitialised value(s)
==25442==    at 0x4008F8: getPath(int*, int) (crash.cpp:27)
==25442==    by 0x400B19: dijkstraAlgorithm(int (*) [6], int) (crash.cpp:62)
==25442==    by 0x400B9C: main (crash.cpp:81)

等等。

不要假设这些数组将自动初始化为零 (0):

int distance[6];
bool shortestPath[6];
int path[6];

初始化这些数组，您将消除一些问题(至少)。

引用Initialization of a normal array with one default value .

已更新:为什么它可以在 Mac 上运行很可能只是巧合，如对 Turn off automatic initialization of variables in Xcode