C++: What operations are only possible by the use of pointers

Question

I'm trying to understand the advantage of pointers. I know the definition and how to create one, but I still don't understand why they are powerful.

So can someone give me an example of something that you can only do with pointers.
I hear Python doesn't have pointers, does this mean that there are operations that can't be done using Python--I mean programming-wise, not just accessing a specific memory location and value? Examples?

Here: http://stackoverflow.com/questions/5727/what-are-the-barriers-to-understanding-pointers-and-what-can-be-done-to-overcome/5754#5754 — Vaibhav Desai, Nov 10 '12 at 18:25
Or here: http://stackoverflow.com/questions/162941/why-use-pointers — Vaibhav Desai, Nov 10 '12 at 18:26
Or here: http://stackoverflow.com/questions/1081519/why-does-c-use-pointers?rq=1 — Vaibhav Desai, Nov 10 '12 at 18:28

score 0 · Answer 1 · answered Nov 10 '12 at 18:26

Pointers are primarily a mechanism to implement reference semantics. If you want to refer to an existing object that lives somewhere else, then you can do so by passing a pointer to that object around.

Without pointers, you could only pass copies of objects around. This would allow you to communicate values, but you couldn't modify an existing object. (Unless your language offered native reference handling, like C++ does, of course.)

As a test, imagine how you would implement the following code:

var a = 10;
var b = 20;

my_magic_swap(a, b);  // how to do this?!

assert(a == 20 && b == 10);

(The answer is of course that my_magic_swap should accept pointers (or equivalent) to the original variables.)

C++: What operations are only possible by the use of pointers

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