C++ equivalent of Java's toString?

In C++ you can overload operator<< for ostream and your custom class:

class A {
public:
  int i;
};

std::ostream& operator<<(std::ostream &strm, const A &a) {
  return strm << "A(" << a.i << ")";
}

This way you can output instances of your class on streams:

A x = ...;
std::cout << x << std::endl;

In case your operator<< wants to print out internals of class A and really needs access to its private and protected members you could also declare it as a friend function:

class A {
private:
  friend std::ostream& operator<<(std::ostream&, const A&);
  int j;
};

std::ostream& operator<<(std::ostream &strm, const A &a) {
  return strm << "A(" << a.j << ")";
}

You can also do it this way, allowing polymorphism:

class Base {
public:
   virtual std::ostream& dump(std::ostream& o) const {
      return o << "Base: " << b << "; ";
   }
private:
  int b;
};

class Derived : public Base {
public:
   virtual std::ostream& dump(std::ostream& o) const {
      return o << "Derived: " << d << "; ";
   }
private:
   int d;
}

std::ostream& operator<<(std::ostream& o, const Base& b) { return b.dump(o); }

In C++11, to_string is finally added to the standard.

http://en.cppreference.com/w/cpp/string/basic_string/to_string