$ cat overloading.cpp

  
CPP / C++ / C Code:
  
#include <iostream>

using namespace std;

class foo {
    int v;
public:
    foo(int i)  { v = i; }
    int value() const  { return v; }
};

ostream& operator<<(ostream&, const foo&);

int
main() {
    foo f(8);

    cout << f << endl;

    return 0;
}

ostream&
operator<<(ostream &out, const foo &f) {
    return out << "(" << f.value() << ")";;
}

$ g++ -Wall overloading.cpp
$ ./a.out
(8)
$