c++ struct 值似乎会自行改变

Question

我只运行了一个简单的代码，但我不断收到“进程完成，退出代码 139（被信号 11 中断：SIGSEGV）” 做一些调试，我发现edges[0].start的值不知何故变成了-2147483644。我发现这种行为很难解释，并且仍然试图找出我在哪里弄错了，但我什至没有更新任何边缘值！无论如何，您能给我的任何提示都会受到极大的重视。您将在下面找到代码。 提前致谢！ 温馨的祝福

#include <stdio.h>
#include <climits>
#include "Utils.h"

struct edge {
    int start;
    int end;
    int weight;
};

int main() {
    int n = 4;
    int m = 4;
    edge edges[4] = {
            {2,4,5},
            {4,1,6},
            {1,3,8},
            {3,2,-3}
    };
    int v,e;
    int distance[4];
    // Step 1: initialize graph
    for(v = 0; v < n; v++){
        distance[v] = INT_MAX;
    }
    distance[0] = 0; //source

    // Step 2: relax edges repeatedly
    for(v = 0; v < n; v++){
        for(e = 0; e < m; e++){
            if(distance[edges[e].start] + edges[e].weight < distance[edges[e].end] ){ //relax
                distance[edges[e].end] = distance[edges[e].start] + edges[e].weight;
            }
        }
    }
    // Step 3: check for negative-weight cycles
    for(e = 0; e < m; e++) {
        if (distance[edges[e].start] + edges[e].weight < distance[edges[e].end]) { //shouldn't be able to relax
            std::cout << "Negative cycle detected, please declare war to Paraguay";
        }
    }
    for(v = 0; v < n; v++){
        std::cout << distance[v] << std::endl;
    }
    return 0;
}

Answer 1

您的 'n' 和 'm' 迭代器变量定义为 4，但 'edges' 数组的索引介于 0 和 3 之间。您的循环将尝试访问边 [4]，从而导致索引超出范围和未定义的行为，这可能是您的起始值损坏的原因。

Answer 2

我实际上不知道为什么，但这对我有用：

#include <iostream>

struct edge {
    int start;
    int end;
    int weight;
};

int main() {
    int n = 4;
    int m = 4;

    const edge edges[4] = {
            {2,4,5},
            {4,1,6},
            {1,3,8},
            {3,2,-3}
    }; /* <= for my surprise, I'm not get error with this
        *    for indexes of distance[something]
        */
    int v,e;
    int distance[4];
    // Step 1: initialize graph
    for(v = 0; v < n; v++){
        distance[v] = 214748364; // <== with this get fixed
    }
    distance[0] = 0; //source

    // Step 2: relax edges repeatedly
        for(v = 0; v < n; v++){
            for(e = 0; e < m; e++){
                if(distance[edges[e].start] + edges[e].weight < distance[edges[e].end] ){ //relax
                    distance[edges[e].end] = distance[edges[e].start] + edges[e].weight;
                }
            }
        }
        // Step 3: check for negative-weight cycles
        for(e = 0; e < m; e++) {
            if (distance[edges[e].start] + edges[e].weight < distance[edges[e].end]) { //shouldn't be able to relax
                std::cout << "Negative cycle detected, please declare war to Paraguay";
            }
        }
        for(v = 0; v < n; v++){
            std::cout << distance[v] << std::endl;
        }
    return 0;
}

而不是使用distance[v] = INT_MAX; 只需使用distance[v] = 214748364; 或不那么接近INT_MAX 的东西，我得到这个输出：

0
8
13
16
Press <RETURN> to close this window...

Answer 3

您已经定义了大小为 4 的距离变量

int distance[4];

虽然边数组的值为：

 edge edges[4] = {
            {2,4,5},
            {4,1,6},
            {1,3,8},
            {3,2,-3}
    };

您正在使用 edge structure 的值来访问每个 distance array. 的单元格 edge 的取值范围是 -3 到 8，而 distance 的取值范围是 0 到 3；这将导致缓冲区溢出并导致应用程序崩溃。