Question

我正在使用指针实现用于图形的C ++程序。这是代码：


#include <iostream>
#include <sstream>
using namespace std;

// Data structure to store Adjacency list nodes
struct Node {
    string source,destination;
    int cost;
    Node* next;
};

// Data structure to store graph edges
struct Edge {
    string src, dest;
    int weight;
    Edge* edge;
};

class Graph
{
    // Function to allocate new node of Adjacency List
    Node* getAdjListNode(string src, string dest, int weight, Node* head)
    {
        Node* newNode = new Node; //create and allocate node
        newNode->source = src;
        newNode->destination = dest;
        newNode->cost = weight;

        // set next of new node as head
        newNode->next = head;
        //move the head to point to the new node
        head = newNode;

        return newNode;
    }

    int N;
    int n; // number of nodes in the graph

public:

    // An array of pointers to Node to //represent
    // adjacency list
     Node **head;

    // Constructor
    Graph(Edge edges[], int e, int v)
    {
        int N=5;
        int n=5;
        // allocate memory
        //Edge *head;
        head = new Node*[N];
        this->N = N;

        // initialize head pointer for all vertices
        for (int i = 0; i < N; i++)
            head[i] = nullptr;

        // add edges to the directed graph
        for (int i = 0; i < n; i++)
        {
            string src = edges[i].src;
            string dest = edges[i].dest;
            int weight = edges[i].weight;

            // insert in the beginning
            Node* newNode = getAdjListNode(src, dest, weight, head[i]);

            // point head pointer to new node
            head[i] = newNode;
        }
    }

    // Destructor
    ~Graph() {
        for (int i = 0; i < N; i++)
            delete[] head[i];

        delete[] head;
    }
};

// print all neighboring vertices of given vertex
void printList(Node* ptr)
{
    while (ptr != nullptr)
    {
        cout << "(" << ptr->from << ", " << ptr->to
            << ", " << ptr->cost << ") ";

        ptr = ptr->next;
    }

    cout << endl;
}

// Graph Implementation in C++ without using STL
int main()
{
    // array of graph edges as per above diagram.
    Edge edges[] =
    {
        // (x, y, w) -> edge from x to y having weight w
        { "aaa","bbb",7 }, { "aaa","ccc",12 }, { "bbb","ddd",9 }, { "eee","ddd",1 },
        { "eee","ccc",14 }
    };


    // Number of vertices in the graph
    int N = 5;

    // calculate number of edges
    int n = sizeof(edges)/sizeof(edges[0]);

    // construct graph
    Graph graph(edges, n, N);

    // print adjacency list representation of graph
    for (int i = 0; i < N; i++)
    {
        // print all neighboring vertices of vertex i
        printList(graph.head[i]);
    }

    return 0;
}

我设法运行了代码并获得了所需的输出，但是出现了一个错误，段错误（核心转储）进程退出，代码为139 。从我读到的内容来看，这与非法指针访问有关，但是我仍然不能完全查明这里的错误。有人可以帮我吗？谢谢。

Answer 1

您将delete[]用于由new分配的指针。在这里

~Graph() {
    for (int i = 0; i < N; i++)
        delete[] head[i];

    delete[] head;
}

应该是

~Graph() {
    for (int i = 0; i < N; i++)
        delete head[i];

    delete[] head;
}

delete应该是在分配了new时使用的，而delete[]应该是在分配了new[]时使用的。

为什么我的代码包含错误分段错误（核心已转储）？

1 个答案: