Can't assign a new object to pointer pointer type in cpp

Question

Assigning a new object to a pointer pointer type in cpp crushes the program. Code looks like this:

#include <iostream>
using namespace std;
struct Node{
    int key;
    Node * nex;
};
int main(){
    Node * my_node = new Node;
    Node ** pp_node;
    *pp_node = my_node;

    return 0;
}

I think that the issue here is following: pp_node is null and by typing *pp_node = my_node; I am trying to dereference null but the question is how can I assign my_node to the pointer, pp_node is pointing at?

Answer 1

pp_node should contain the address of my_node , in order to have pp_node point at my_node(which is itself a pointer and holding an address).

#include <iostream>

    struct Node{
    int key_;
    Node * nex;
};

int main(){
    Node node={34, nullptr};
    Node* p_my_node = &node;
    Node** pp_node;
    pp_node = &p_my_node;
    std::cout<<(**pp_node).key_;
    return 0;
}

Now

• p_my_nodeis a piece of memory whose value(data it is holding) is address of node. So it points at node
• pp_node is a piece of memory whose value is address of p_my_node, So it points at p_my_node

the output of the code above is 34, as we expected.