#include <iostream>
#include <cstdlib>
using namespace std;

struct str {
	int f1;
	int f2;
};

void f(str copy, str *p, const str& r);

int main()
{
	str a1 = {10, 20};
	str a2 = {30, 40};
	str a3 = {50, 60};

	f(a1, &a2, a3);

	cout << "a1.f1 == " << a1.f1 << "\n"
		<< "a2.f1 == " << a2.f1 << "\n"
		<< "a3.f1 == " << a3.f1 << "\n";

	return EXIT_SUCCESS;
}

void f(str copy, str *p, const str& r)
{
	++copy.f1;   //has no effect on a1.f1; means copy.f1 = copy.f1 + 1
	++p->f1;     //adds 1 to a2.f1; means p->f1 = p->f1 + 1
	//++r.f1;    //won't compile
}