如何在 C++ 中创建动态数组？它因分段错误而崩溃

Question

我已经看到这里有一个非常相似的问题：Dynamic array in C cause segmentation fault 它是在 C 上使用 malloc 的，我不明白答案。 我开始学习编程，我刚开始学习数组，恐怕我不太了解它是如何工作的。 我正在尝试创建一个方形动态数组。我正在尝试使用指针和'new'来指向一个var来获取它的大小。 我不明白为什么我的代码（编译时没有警告）不起作用，它在用户输入大小值后崩溃。 这就是我所拥有的：

int main(){

    int **dyn_array=nullptr; //dynamic multidimensional array pointer to pointer

    int *rows_cols=nullptr; //pointer to var with number of rows that wil be introduced by the user 

    int n_elements=0;

    rows_cols = &n_elements;    //now the pointer points to memory location of var with number of rows/cols

    dyn_array = new int *[n_elements];          //pointer of array now points to pointer of rows/cols var to get its size

    cout << "ENTER A EVEN NUMBER OF ELEMENTS FOR A SQUARE ARRAY: " << endl;
    cin >> *rows_cols;  //the value entered by the user its assigned by the pointer to var that its assigned as size of the array

    dyn_array[n_elements][n_elements]={0}; //It crashes. Why? I don't understand...

   return 0;
}

非常感谢。 （对不起，我的英语，我还在学习）。

Answer 1

代码存在三个问题：

1. C++ 数组从索引 0 开始，使用 n_elements 索引数组会导致非一访问错误。

dyn_array = new int *[n_elements]; 
dyn_array[n_elements] 

1. dyn_array 指向一个大小为 0 的 int 数组

int n_elements=0;
dyn_array = new int *[n_elements]; 

1. 第二个n_elements 索引dyn_array[n_elements] 指向的数组，该数组不存在。

dyn_array[n_elements][n_elements]={0};

修复

int main(){

    int **dyn_array=nullptr; //dynamic multidimensional array pointer to pointer

    int *rows_cols=nullptr; //pointer to var with number of rows that wil be introduced by the user 

    int n_elements=0;

    rows_cols = &n_elements;    //now the pointer points to memory location of var with number of rows/cols

    cout << "ENTER A EVEN NUMBER OF ELEMENTS FOR A SQUARE ARRAY: " << endl;
    cin >> *rows_cols;  //the value entered by the user its assigned by the pointer to var that its assigned as size of the array

    dyn_array = new int *[n_elements];          //pointer of array now points to pointer of rows/cols var to get its size

    for (int i = 0; i < n_elements; ++i) 
       dyn_array[i] = new int [n_elements];

    dyn_array[n_elements-1][n_elements-1]={0}; //It crashes. Why? I don't understand...

   return 0;
}

Answer 2

您为int 指针的空数组分配了空间。空，因为n_elements 在分配时为零。您还需要通过添加像dyn_array[0] = new int[size]; 这样的行来为dyn_array 的元素分配空间。

但是，最好尝试std::vector<int>，而不是搞乱动态内存分配。