Why use pointers in C++?

Question

I am learning C++ from a game development standpoint coming from long time development in C# not related to gaming, but am having a fairly difficult time grasping the concept/use of pointers and de-referencing. I have read the two chapters in my current classes textbook literally 3 times and even googled some different pages relating to them, but it doesn't seem to be coming together all that well.

I think I get this part:

#include <iostream>

int main()
{
    int myValue   = 5;
    int* myPointer = nullptr;

    std::cout << "My value: " << myValue << std::endl; // Returns value of 5.
    std::cout << "My Pointer: " << &myValue << std::endl; // Returns some hex address.

    myPointer  = &myValue; // This would set it to the address of memory.
    *myPointer = 10; // Essentially sets myValue to 10.

    std::cout << "My value: " << myValue << std::endl; // Returns value of 10.
    std::cout << "My Pointer: " << &myValue << std::endl; // Returns same hex address.
}

I think what I'm not getting is, why? Why not just say myValue = 5, then myValue = 10? What is the purpose in going through the added layer for another variable or pointer? Any helpful input, real life uses or links to some reading that would help make sense of this would be GREATLY appreciated!

Answer 1

The purpose of pointers is something you will not fully realize until you actually need them for the first time. The example you provide is a situation where pointers are not needed, but can be used. It is really just to show how they work. A pointer is a way to remember where memory is without having to copy around everything it points to. Read this tutorial because it may give you a different view than the class book does:

http://www.cplusplus.com/doc/tutorial/pointers/

Example: If you have an array of game entities defined like this:

std::vector<Entity*> entities;

And you have a Camera class that can "track" a particular Entity:

class Camera
{
private:
   Entity *mTarget;  //Entity to track

public:
   void setTarget(Entity *target) { mTarget = target; }
}

In this case, the only way for a Camera to refer to an Entity is by the use of pointers.

entities.push_back(new Entity());
Camera camera;
camera.setTarget(entities.front());

Now whenever the position of the Entity changes in your game world, the Camera will automatically have access to the latest position when it renders to the screen. If you had instead not used a pointer to the Entity and passed a copy, you would have an outdated position to render the Camera.