Question

I am trying:

class MyClass {
public:
    MyClass();

    int myID;
    static int currentID;
};

MyClass::MyClass() {
    myID = currentID;
    ++currentID;
}

I’m trying to assign a unique ID to all the instances of this class.

Edit:

It doesn’t work for me. I get two of these in xcode:

Undefined symbols:
“GameObject::currentID”, referenced from:
__ZN10GameObject9currentIDE$non_lazy_ptr in GameObject.o
(maybe you meant: __ZN10GameObject9currentIDE$non_lazy_ptr)
ld: symbol(s) not found
collect2: ld returned 1 exit status

Answer 1

It works for me:

#include <iostream>

class My
{
    public:
    My() : id(++currentId) {}

    int id;
    static int currentId;
};

int My::currentId = 0;

std::ostream & operator<<(std::ostream & os, My & m)
{
    return os << m.id;
}

int main()
{
    My a;
    My b;
    My c;

    std::cout << a << std::endl;
    std::cout << b << std::endl;
    std::cout << c << std::endl;
}

Output:

> ./x
1
2
3