Problem with overloading input operator in c++ - c++

Question

I started to learn C++ recently and i ran into this trouble with using overloaded input operator >>.
I am writing a class to describe a Complex number.
My problem is: If i put my main() in the Complex.cpp, my program run normally. But if i create a new file main.cpp and put my main() there i ran into error.
error: invalid operands to binary expression ('std::istream' (aka 'basic_istream') and 'Complex')
candidate function not viable: no known conversion from 'std::istream' (aka 'basic_istream') to 'std::istream *' (aka 'basic_istream *') for 1st argument; take the address of the argument with &
(There are a lots more error bellow but they point to istream so i don't think that is the problem)
This is my header file:
#include <iostream>
using namespace std;
#ifndef HEADER_H
#define HEADER_H
#endif // HEADER_H
class Complex
{
public:
double _real;
double _imag;
public:
Complex(double, double);
double getReal() const;
double getImag() const;
void setReal(double);
public:
Complex operator=(const Complex&);
Complex * operator+(const Complex&);
Complex * operator+(const double&);
friend Complex * operator+(const double&, const Complex&);
Complex * operator++();
Complex * operator++(int);
Complex * operator--();
Complex * operator--(int);
operator double() const;
friend ostream &operator<<(ostream*, const Complex&);
friend istream &operator>>(istream*, Complex&);
};
And i created Complex.cpp to identify the function:
#include "Complex.h"
using namespace std;
Complex::Complex(double a, double b)
{
this->_real = a;
this->_imag = b;
}
double Complex::getReal() const{...}
void Complex::setReal(double x){...}
double Complex::getImag() const{...}
Complex Complex::operator=(const Complex& other){...}
Complex * Complex::operator+(const Complex& other){...}
Complex * Complex::operator+(const double &other){...}
Complex * operator+(const double &first, const Complex &second){...}
Complex * Complex::operator++(){...}
Complex * Complex::operator++(int){...}
Complex * Complex::operator--(){...}
Complex * Complex::operator--(int){...}
Complex::operator double() const{...}
ostream &operator<<(ostream &output, const Complex &comp)
{
output << comp._real << " + " << comp._imag << "i";
return output;
}
istream &operator>>(istream &input, Complex &comp)
{
input >> comp._real >> comp._imag;
return input;
}
This is my main:
#include "Complex.h"
int main()
{
Complex com4(0,0);
cout << "Input Complex: ";
cin >> com4;
cout << com4 <<endl;
}

Answer 1

You declared io operators with pointers (which is wrong)
friend ostream &operator<<(ostream*, const Complex&);
friend istream &operator>>(istream*, Complex&);
but implemented it correctly with references.
friend ostream &operator<<(ostream&, const Complex&) {...}
friend istream &operator>>(istream&, Complex&) {...}
When you have your main() in Complex.cpp, the compiler can see those correct implementations (that are not defined in any header).
If you have your main() somewhere else, the compiler can only see the declarations in the header, which have the wrong signature.
Solution will be to fix the declarations of operator<< and operator>> in the header, so that they match the implementation.
As a note and as already mentioned in the comments: Your other operator-overloads should return Complex & or Complex not Complex *. Take a look at std::complex or this page, detailing operator overloading to see what the canoncial implementations look like.