向量类实现上的分段错误

Question

对于许多编码测试，STL 是不允许的，所以我正在尝试实现向量类。为了表示该图，我使用邻接表。它在

new_allocation

方法中给了我分段错误。有时，当我运行代码时，我会得到正确的输出，但当我调试时，我会得到 SegFault。 以下是我的代码。

#include <iostream>
using namespace std;

template <typename T> class vector{
    T *arr;
    int s;
    int c;
    void new_allocation(){
        T *temp = new T[s + 10];       // SEGMENTATION FAULT HERE
        c = s + 10;
        for (int i = 0; i < s; i++)
            temp[i] = arr[i];
        arr = temp;
        delete[] temp;
    }
    public:
        vector() { s = c = 0; }
        vector(int userVectorSize){
            s = c = userVectorSize;
            arr = new T[userVectorSize];
        }
        void push_back(T data){
            if (s == c)
                new_allocation();
            arr[s] = data;
            s++;
        }
        T operator[](int index){ return arr[index]; }
        int size() { return s; }
};

int main(){
    int n, m;
    cin >> n >> m;
    vector<int> graph[n + 1];

    for (int i = 0; i < m; i++){
        int v1, v2;
        cin >> v1 >> v2;
        graph[v1].push_back(v2);
        graph[v2].push_back(v1);
    }

    for (int i = 1; i <= n; i++){
        cout << i << " -> ";
        for (int k = 0; k < graph[i].size(); k++)
            cout << graph[i][k] << " ";
        cout << endl;
    }
}

Answer 1

这永远行不通

     arr = temp;
    delete[] temp;

将“temp”指针放入 arr（数据元素的工作缓冲区）中，然后将其删除，因此 arr 指向已删除的内存

Answer 2

1. 请初始化默认ctor中的

   arr

   ：

    vector() {
        s = c = 0;
        arr = nullptr; // (1)
    }

2. 正如pm100提到的，请挑选正确的阵列到

   delete[]

   。

    void new_allocation() {
        T *temp = new T[s + 10]; // SEGMENTATION FAULT HERE
        c = s + 10;
        for (int i = 0; i < s; i++)
            temp[i] = arr[i];

        // (2)
        if (arr != nullptr) {
            delete[] arr;
        }
        arr = temp;
    }

原因是你的

arr

默认指向任意内存，所以当你尝试

delete[] arr

时它仍然会报告分段错误。

#include <iostream>
using namespace std;

template <typename T> class vector {
    T *arr;
    int s;
    int c;
    void new_allocation() {
        T *temp = new T[s + 10]; // SEGMENTATION FAULT HERE
        c = s + 10;
        for (int i = 0; i < s; i++)
            temp[i] = arr[i];

        if (arr != nullptr) {
            delete[] arr;
        }
        arr = temp;
    }

  public:
    vector() {
        s = c = 0;
        arr = nullptr;
    }
    vector(int userVectorSize) {
        s = c = userVectorSize;
        arr = new T[userVectorSize];
    }
    void push_back(T data) {
        if (s == c)
            new_allocation();
        arr[s] = data;
        s++;
    }
    T operator[](int index) { return arr[index]; }
    int size() { return s; }
};

int main() {
    int n, m;
    cin >> n >> m;
    vector<int> graph[n + 1];

    for (int i = 0; i < m; i++) {
        int v1, v2;
        cin >> v1 >> v2;
        graph[v1].push_back(v2);
        graph[v2].push_back(v1);
    }

    for (int i = 1; i <= n; i++) {
        cout << i << " -> ";
        for (int k = 0; k < graph[i].size(); k++)
            cout << graph[i][k] << " ";
        cout << endl;
    }
}

Answer 3

你应该删除 arr 而不是 temp:

    void new_allocation(){
        T *temp = new T[s + 10];       // SEGMENTATION FAULT HERE
        c = s + 10;
        for (int i = 0; i < s; i++)
            temp[i] = arr[i];
        delete[] arr;
        arr = temp;
    }