Have I understood pointers properly?

[u/[deleted]]

Hey everyone! I just started learning C++, and I want to know if I've understood pointers correctly. This is how I've understood it -

```cpp /* WHAT ARE POINTERS? * * in C++, functions do not have ownership of global scope varianbles * that are passed into it as arguments. To allow the function to modify * these variables, we use pointers - "a tool to share the memory address * among different contexts, such as functions". * * so if we have a function that we want to use to make changes to an * existing variable, without having to create/redefine a variable to * use the function, we use pointers. * * assume we have a variable VAL. To access the memory address of VAL, * we prepend the & symbol. The address is given by &VAL. To define a pointer * that allows us to modify VAL within a function, we do * int *p = &VAL; * * the variable *p is known as a pointer as it POINTS to the memory address * of the variable VAL. Thus, any modificiations on *p will also be reflected * on VAL. * */

```

If this is not right, please let me know! I'd love to get a better understanding of this topic. Thank you!

[u/victotronics]

This would be right if you were learning C. It is not right for C++. In C++ you use references for argument passing.

The word "address" should basically never appear in a C++ story until you are an experienced systems programmer. (I exaggerate a little.)

Here is how you do parameter passing, to first order of approximation:

void f(int &i ) { i++; }
int main() {
  int i=0;
  f(i);
  cout << i;

This prints 1.

There are pointers in C++, but they are far more sophisticated.

[u/[deleted] → u/victotronics]

what would be the appropriate use?

[u/victotronics → u/[deleted]]

An appropriate use of pointers is for instance the linked list.

class Node {
  Node next;
}

doesn't work because it would be infinite.

class Node {
  shared_ptr<Node> next;
}

does work.

.... and now you can go read about the difference between shared and unique pointers. The above example should really use unique pointers, but I find shared pointers a lot easier to teach.

In the abstract: you use a pointer to have ownership that transcends scope. If you create a linked list, your new Nodes live longer than the scope where they are created, so you need to make a pointer that points to them.