multiple definition in header file
- by Jérôme
Here is a small code-example from which I'd like to ask a question :
complex.h :
#ifndef COMPLEX_H
#define COMPLEX_H
#include <iostream>
class Complex
{
public:
Complex(float Real, float Imaginary);
float real() const { return m_Real; };
private:
friend std::ostream& operator<<(std::ostream& o, const Complex& Cplx);
float m_Real;
float m_Imaginary;
};
std::ostream& operator<<(std::ostream& o, const Complex& Cplx) {
return o << Cplx.m_Real << " i" << Cplx.m_Imaginary;
}
#endif // COMPLEX_H
complex.cpp :
#include "complex.h"
Complex::Complex(float Real, float Imaginary) {
m_Real = Real;
m_Imaginary = Imaginary;
}
main.cpp :
#include "complex.h"
#include <iostream>
int main()
{
Complex Foo(3.4, 4.5);
std::cout << Foo << "\n";
return 0;
}
When compiling this code, I get the following error :
multiple definition of operator<<(std::ostream&, Complex const&)
I've found that making this fonction inline solves the problem, but I don't understand why. Why does the compiler complain about multiple definition ? My header file is guarded (with #define COMPLEX_H).
And, if complaining about the operator<< fonction, why not complain about the public real() fonction, which is defined in the header as well ?
And is there another solution as using the inline keyword ?
