指向指针的动态内存管理（C ++）

Question

I need some help. I have an array of pointers:

 int *ptr = new int[N]; 

I want a two dimensional array of pointers, which points to that one dimensional array. I know how to allocate memory for a two dimensional pointer:

 int (*nn)[4] = new int [N][4]; 

BUT: How to allocate memory for a two dimensional pointer to a pointer? Is that possible anyway?

I need to define neighbors on a grid. Finally the connection should be like this:

 for (int Vertex = 0; Vertex < N; ++Vertex) { nn[Vertex][0] = ptr[(Vertex + 1) % N]; nn[Vertex][1] = ptr[(Vertex + N - 1)% N]; nn[Vertex][2] = ptr[(Vertex + L) % N]; nn[Vertex][3] = ptr[(Vertex + N - L) % N]; if (Vertex % L == 0) { nn[Vertex][1] = ptr[Vertex + L - 1]; } if((Vertex + 1)%L == 0){ nn[Vertex][0] = ptr[Vertex - L + 1]; } } 

I just got stuck in allocating the memory...

Answer 1

If you want a two dimensional array of pointers to int, you actually need a pointer to a pointer to a pointer to int, and you need to allocate the memory in a for-loop, like this:

int *** nn = new int**[N];
for(int i=0; i<N; i++) nn[i] = new int*[4];

Now nn[x][y] is a pointer to an int and *(nn[x][y]) is an int.

It is true what the comments say, though, ptr is not an array of pointers. However, you can still make nn point to the values of ptr by doing this:

nn[x][y] = ptr+index;

and NOT:

nn[x][y] = ptr[index];