One object accessible across all my application classes

I would like to have an object accessible across all my application classes. So I though:

#include <iostream>

using namespace std;

class MyClass {
public:
    MyClass(){}
    int id(){return -1;}
};

extern const MyClass myClass;

int main() {
    cout << myClass.id();
    return 0;
}

And anywhere I need it, I'll do:

extern const MyClass myClass;

and just use it, like:

cout << myClass.id();

But, I was wrong. That returns error:

error: passing 'const MyClass' as 'this' argument of 'int MyClass::id()' discards qualifiers [-fpermissive]

I Guess I could do static MyClass myClass;, instead. And so I will have more or less the same functionality.

What's the best/correct approach?