Question

Can I overload existing function/operator in existing class?

I was trying to do:

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

string& string::operator<<(const string& str) {
  this->append(str);
}

But this gives me error:

test.cpp:5: error: too few template-parameter-lists

How can I do this? Or I can’t?

Answer 1

You can’t add member functions to a class unless you modify that class’ definition. Use a free function instead:

string& operator<<(string & lhs, const string & rhs) {
    return lhs += rhs;
}