gistfile1.cpp

#include <iostream>

class Barney {
	int age;
public:
	Barney() { age = 42; }
	Barney& operator++() {
		age++;
		std::cout << "Barney is " << age << " years old." << std::endl;
		return *this;
	}
};

Barney make_barney() {
	return Barney();
}

Barney const make_barney_const() {
	return Barney();
}

int main(void) {
	++make_barney();
	//++make_barney_const();  // error: passing ‘const Barney’ as ‘this’ argument of ‘Barney& Barney::operator++()’ discards qualifiers [-fpermissive]
	return 0;
}