Edit where a pointer points within a function

Question

I have a pointer to a struct object in C++.

 node *d=head;

I want to pass that pointer into a function by reference and edit where it points. I can pass it but it doesn't change where the initial pointer points but only the local pointer in the function. The arguments of the function must be a pointer right? And after how do I change it to show to a different object of the same struct?

Answer 1

You have two basic choices: Pass by pointer or pass by reference. Passing by pointer requires using a pointer to a pointer:

void modify_pointer(node **p) {
    *p = new_value;
}

modify_pointer(&d);

Passing by reference uses &:

void modify_pointer(node *&p) {
    p = new_value;
}

modify_pointer(d);

If you pass the pointer as just node *d, then modifying d within the function will only modify the local copy, as you observed.

Answer 2

Pass it by reference:

void foo(node*& headptr)
{
     // change it
     headptr = new node("bla");
     // beware of memory leaks :)
}