C++, good old LNK1169 (and LNK2005) errors

Question

I have 4 files, 2 headers and 2 cpp files.

Header file one:

#ifndef complex_2
#define complex_2
#include
#include

using         


        

Answer 1

Example to repro LNK1169 & LNK2005 with structs: Place the following in the header file:

    Struct Foo
    {
    std::wstring Bar[3]
    };

    Foo InitFoo[2]
    {
    {L"ConstBar1Val", L"ConstBar1Val2", L"ConstBar1Val3"},
    {L"ConstBar2Val", L"ConstBar2Val2", L"ConstBar3Val3"}
    };

Solution: Move the initialised struct & arrays to the corresponding cpp file.

Answer 2

Move the definition of the

std::ostream & operator<< (ostream &mm, const comp::complex &c)

in one of the CPP files.

The linker doesn't like this. Personally I'd create a new cpp file for this one too :)

Answer 3

When you define a standalone function (with a body) in header file you must use inline (functions defined within class definition are inline by default).

E.g. in header file one must be :

inline ostream& operator<< (ostream &mm, const complex &c){
    if(c.get_im() >= 0){
        mm << "(" << c.get_re() << " + " << c.get_im() << "i)" << endl;
    }
    if(c.get_im() < 0){
        mm << "(" << c.get_re() << " - " << -(c.get_im()) << "i)" << endl;
    }
    return mm;
}

Otherwise you will define this function in each translation unit that includes that header and thus may get multiple definition error.