C ++静态成员变量

Question

I have a class header:

class Game {
    static Game instance;
}

And I want to set the 'instance' to the "this" object on instantiation, but can't get it to work.

Here's my implementation:

Game::Game() {
    Game::instance = this;
}

Visual Studio gives a red squiggly thing on the = 's operator saying:

Error: no operator "=" matches these operands
operands are types are: Game = Game *

---

Update
I didn't understand the error but I tried changing the assignment code to this:

Game::instance = * this;

And the error went away.

So, now I'm wondering, what is the difference between those two assignment statements?

I think II sort of know... but an explanation would be nice.

Answer 1

Sounds like you're going for the singleton pattern! Search it for some reading. Some people don't like it and I've never had a use for it but if you want it then you'll need more of a framework than you have. Note that this doesn't exist until you have created an object. Also be careful, if you use =*this you will be making a copy.

If you want your instance to be available from the start of the program then you perhaps should just declare a global instance of the class, it's easier and safer. The singleton pattern is for when you want delayed instantiation or optional instantiation of your class.

Answer 2

Should be

static Game* instance; // a pointer

Now instance points to the newly created instance.

If you instead do this:

Game::instance = *this;

instance is assigned a 'snapshot' of the current state of the new object. This is probably not what you want.

Answer 3

instance is an Object. this is a pointer to your current Object. By using * this , you are dereferencing your pointer, hence returning the pointee (= the current object)