how to use std in code without including “using namespace std”?

Question

In this code of operator Overloading, i don't want to write "using namespace std" instead i want to include "std::" wherever required.

After adding "std::" after cout and cin, i am still getting Errors where else to include "std::".

#include<iostream>
//using namespace std;
class Complex
{
private:
  int real, imag;
public:
  Complex(int r = 0, int i = 0) : real(r), imag(i) {}

  friend ostream & operator << (ostream &, const Complex &);
  friend istream & operator >> (istream &, Complex &);
};

ostream & operator << (ostream &out, Complex &obj)
{
  out<<obj.real<<" "<<obj.imag;
  return out;
}
istream & operator >> (istream &in, const Complex &obj)
{
  in>>obj.real>>obj.imag;
  return in;
}

int main()
{
  Complex obj;
  std::cin>>obj;
  std::cout<<obj;
  return 0;
}

It should take input two numbers using istream operator and output two numbers using ostream operator.

Stack Danny Stack Danny · Accepted Answer · 2019-01-25T12:25:28

add std:: to ostream and istream

They come from the headers <istream> and <ostream> and are defined in <iosfwd>

#include<iostream>
//using namespace std;
class Complex
{
private:
    int real, imag;
public:

    Complex(int r = 0, int i = 0) : real(r), imag(i) {}

    friend std::ostream& operator<<(std::ostream& out, const Complex& obj);
    friend std::istream& operator>>(std::istream& in, Complex& obj);
};

std::ostream& operator<<(std::ostream &out, const Complex &obj)
{
    out << obj.real << " " << obj.imag;
    return out;
}
std::istream& operator>>(std::istream &in, Complex &obj)
{
    in >> obj.real >> obj.imag;
    return in;
}

int main()
{
    Complex obj;
    std::cin >> obj;
    std::cout << obj;
    return 0;
}

(not related to the std:: problem) You can also access your private variables outside the class without the friend declaration by using get/set member functions. Thanks to @aschepler for pointing out my mistake regarding the accessibility.

#include<iostream>
class Complex
{
private:
    int real, imag;
public:
    int get_real() const {
        return real;
    }
    void set_real(int real) {
        this->real = real;
    }
    int get_imag() const {
        return imag;
    }
    void set_imag(int imag) {
        this->imag = imag;
    }

    Complex(int r = 0, int i = 0) : real(r), imag(i) {}

};

std::ostream& operator<<(std::ostream &out, const Complex &obj)
{
    out << obj.get_real() << " " << obj.get_real();
    return out;
}
std::istream& operator>>(std::istream &in, Complex &obj)
{
    int real, imag;
    in >> real >> imag;
    obj.set_real(real);
    obj.set_imag(imag);
    return in;
}

int main()
{
    Complex obj;
    std::cin >> obj;
    std::cout << obj;
    return 0;
}

how to use std in code without including “using namespace std”?

3 Answers