C++ insertion operator for class method - c++

Question

In C++ is there a way to use the insertion operator for a class method?
This operator<< overload is working:
class Complex {
public:
//Normal overload:
friend std::ostream& operator<<(std::ostream &out, const Complex &o) {
out << "test overload";
return out;
}
Complex() {};
~Complex() {};
};
I can do this:
int main()
{
Complex* o = new Complex();
std::cout << "This is test: " << *o << "." << std::endl; // => This is test: test overload.
}
I know about stream manipulators, like this:
std::ostream& welcome(std::ostream& out)
{
int data = 1;
out << "WELCOME " << data << "\r\n";
return out;
}
int main()
{
std::cout << "Hello " << welcome; // => "Hello WELCOME 1\r\n"
}
How can I put the welcome method into the Complex class and then how shall I call it from cout (please note that welcome method must access some class member variables)?
My trial:
class Complex {
public:
//Normal overload:
friend std::ostream& operator<<(std::ostream &out, const Complex &o) {
out << "test overload";
return out;
}
std::ostream& welcome(std::ostream& out) {
out << "WELCOME " << data << "\r\n";
return out;
}
Complex() { data = 1; };
~Complex() {};
private:
int data;
};
int main()
{
Complex* o = new Complex();
std::cout << "This is test2: " << o->welcome << std::endl; // compile error
}

Answer 1

One easy way to pick a different << overload is to use a different type.
#include <iostream>
class Complex {
public:
//Normal overload:
friend std::ostream& operator<<(std::ostream &out, const Complex &o) {
out << "test overload";
return out;
}
struct extra_info {
const Complex& parent;
extra_info(const Complex& p) : parent(p) {}
friend std::ostream& operator<<(std::ostream& out, const extra_info& ei){
int i = 1;
out << "extrainfo " << i;
return out;
}
};
extra_info extrainfo() {
return {*this};
}
Complex() {};
~Complex() {};
};
int main() {
Complex c;
std::cout << c << "\n";
std::cout << c.extrainfo();
}
Output:
test overload
extrainfo 1
I suppose in your real code you are using members. Hence the helper type must hold a reference to the Complex instance.