[C++11] sizeof

We usually use the sizeof to evaluate the size of a instance (class or struct) or variable. Such as:

class Car {
public:
    int id;
    string name;
    static int count;
};

int main() {
    Car p;
    cout << sizeof(p) << endl;           // 4
    cout << sizeof(Car::count) << endl;  // 4
    return 0;
}

In C++98, we can not evaluate the size of id without creating a instance with sizeof, but we can do it with C++11.

//C++98: error: invalid use of non-static data member 'id'
//C++11: 4
cout << sizeof(Car::id) << endl;

In C++98, if we do the same thing, we maybe do something like this:

cout << sizeof(((Car*)0)->id) << endl; // 4

It's very clear to see that the way of C++11 is easier to read.