Pointer to Pointer Use Cases

While pointers to pointers (i.e., int**) can be confusing and are often a sign of complex code, there are some situations where they are necessary or useful:

1. When you need to modify a pointer in a function. If you want a function to be able to modify a pointer passed to it, you need to pass a pointer to that pointer.
2. When working with multidimensional arrays. A 2D array is essentially an array of arrays, so a pointer to a 2D array is a pointer to a pointer.
3. When implementing complex data structures like linked lists or trees, where each node contains a pointer to another node.

Here's an example of a function that modifies a pointer:

1#include <iostream>
2
3void AllocateInt(int** ptr) {
4  *ptr = new int;  // Allocate memory
5  **ptr = 10;      // Set value
6}
7
8int main() {
9  int* p = nullptr;
10  AllocateInt(&p);  // Pass pointer to pointer
11
12  std::cout << "*p = " << *p << "\n";
13
14  delete p;  // Deallocate memory
15}

1*p = 10

In this case, AllocateInt needs to modify the pointer p itself (not just the value it points to), so we need to pass a pointer to p, which is a pointer to a pointer.

However, pointers to pointers can quickly make code harder to understand and maintain, so they should be used judiciously. Often, there are better alternatives like references, smart pointers, or higher-level abstractions.