CODEWITHSUNDEEP
c++headeroperator-overloading
Hubert
Hubert

Reputation: 152

Include operator overloads from another file

I want to use an operator defined in another file and if possible, another namespace as well, here is what I have.

(operators.hpp)

#ifndef __OPERATORS__HPP__
#define __OPERATORS__HPP__

#include "proto_handler.hpp"

#include <iostream>

namespace apius {
namespace support {
namespace operators{

std::istream& operator>>(std::istream& in,
                         inventory::proto::item& item);
}
}
}

(operatos.cpp)

#include "operators.hpp"

namespace apius {
namespace support {
namespace operators{

std::istream& operator>>(std::istream& in,
                         inventory::proto::item& item){
    //code here
}

}
}
}

(another_file.cpp)

#include "operators.hpp"

extern std::istream& operator>>(std::istream& in,
                         inventory::proto::item& item);
void test(){
    inventory::proto::item new_item;
    std::cin>>new_item;
}

and I get undefined reference to operator at line containing std::cin

What can I do to make this work?

Upvotes: 0

Views: 555

Answers (1)

Kirill Korolev
Kirill Korolev

Reputation: 1006

Basically the linker is struggling to find such symbol because there is no one. Because of the C++ name mangling you'll get something like __ZN5apius7support9operatorsrsERNSt3__113basic_istream... in your symbol table in an object file. Notice that the namespace part is also there. But you're telling that there is such operator in a global namespace. As Adrian correctly noticed you can simply add

using namespace apius::support::operators;

Furthermore, what I prefer to do it is to declare a friend operator in a class and then you don't need any usings.

Upvotes: 2

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