strange linking error with operator overloading

Hello everyone,


I am meeting with a strange linking error regarding to operator overloading. I am creating a C++ static lib, and then linking it with a C application. Here is the error message and source codes,

I am using adapter.cpp, adapter.h, foo.cpp and foo.h to create a static lib called foo.lib, then link it with a C application (goo.c). There is no problem to generate the static lib foo.lib.

Any comments to solve this link error?

Code:

---

error LNK2019: unresolved external symbol "private: class FooNameSpace::Foo __thiscall FooNameSpace::Foo::operator=(long)" (??4Foo@FooNameSpace@@AAE?AV01@J@Z) referenced in function "private: __thiscall FooNameSpace::Foo::Foo(
long)" (??0Foo@FooNameSpace@@AAE@J@Z)

fatal error LNK1120: 1 unresolved externals

---

adapter.cpp

Code:

---

#include "adapter.h"
#include "foo.h"

using namespace FooNameSpace;

void compute(void)
{
        Goo g;
        g.computeFoo();
}

---

adapter.h

Code:

---

#ifdef __cplusplus
extern "C" {
#endif

void compute (void);

#ifdef __cplusplus
}
#endif

---

foo.cpp

Code:

---

#include "foo.h"

using namespace FooNameSpace;

Foo Foo::operator=(long value)
{
  this -> value = value;
  return (*this);
}

---

foo.h

Code:

---

namespace FooNameSpace
{
        class Foo
        {

        private:
                long value;
 
                Foo (long value) { (*this) = value; }
                inline Foo operator= (long value);
                friend class Goo;
  };

        class Goo
        {
        public:
                void computeFoo()
                {
                        Foo foo = Foo(0L);
                }
  };
}

---

goo.c (link with foo.lib)

Code:

---

#include "adapter.h"
#include "windows.h"

int WINAPI WinMain (HINSTANCE hInstance, HINSTANCE hPrevInstance,
                    LPWSTR lpCmdLine, int nCmdShow)
{
        compute();
        return 0;
}

---

thanks in advance,
George

You either call the using directive in foo.cpp or use the scope operator on the operator overload. You cant do both.

Quote:

---

Originally Posted by Mario F.

You either call the using directive in foo.cpp or use the scope operator on the operator overload. You cant do both.

---

Huh? One is a namespace, the other is the class name.

Code:

---

/*myn.h */
#ifndef MY_NAMESPACE_H
#define MY_NAMESPACE_H

namespace MY {
  class foo {
    public:
        void bar();
  };
}

#endif

---

Code:

---

/*imp.cpp */
#include <iostream>
#include "myn.h"

using namespace MY;

void foo::bar() // Nothing wrong here
{
    return;
} // you could even requalify it multiple times MY::foo::foo::foo::bar()
// It doesn't matter

---

To the OP, I think your problem is with your extern "C". Try taking it out and see what happens.

Actually you are right. I skimmed through the source code. Bad advice.

Hello Mario,

Quote:

---

Originally Posted by Mario F.

You either call the using directive in foo.cpp or use the scope operator on the operator overload. You cant do both.

---

I am confused. What do you mean "the using directive in foo.cpp" and "use the scope operator"?


regards,
George

Hi SlyMaelstrom,

Quote:

---

Originally Posted by SlyMaelstrom

Huh? One is a namespace, the other is the class name.

Code:

---

/*myn.h */
#ifndef MY_NAMESPACE_H
#define MY_NAMESPACE_H

namespace MY {
  class foo {
    public:
        void bar();
  };
}

#endif

---

Code:

---

/*imp.cpp */
#include <iostream>
#include "myn.h"

using namespace MY;

void foo::bar() // Nothing wrong here
{
    return;
} // you could even requalify it multiple times MY::foo::foo::foo::bar()
// It doesn't matter

---

To the OP, I think your problem is with your extern "C". Try taking it out and see what happens.

---

I have not seen any relationship between your answer and my question.

1. Do you mean I use the same name for a namespace and for a class? As you can see, I am using FooNameSpace as the namespace name and Foo as the class name -- there are no duplicates.

2. I can not remove extern "C" since I am linking foo.cpp, adapter.cpp, adapter.h and foo.h (which will generate a static lib called foo.lib) to a C application (goo.c). If I remove extern "C", C application (goo.c) can not work with C++'s name mangling.


regards,
George

No george. It was a mistake I made based on the linker error and on the fact I just skimmed through your code. My advice was partially wrong.

Anyways, the problem here is that you have your operator declared as inline. Either remove the inline specifier or move the operator definition to the header file.

Quote:

---

Originally Posted by George2

Hi SlyMaelstrom,




I have not seen any relationship between your answer and my question.

1. Do you mean I use the same name for a namespace and for a class? As you can see, I am using FooNameSpace as the namespace name and Foo as the class name -- there are no duplicates.

2. I can not remove extern "C" since I am linking foo.cpp, adapter.cpp, adapter.h and foo.h (which will generate a static lib called foo.lib) to a C application (goo.c). If I remove extern "C", C application (goo.c) can not work with C++'s name mangling.


regards,
George

---

No, the whole namespace issue was not in regards to you, it was in regards to the reply you recieved. I understand that you need to use extern "C", but the issue is that I don't think the C program your linking with likes your overloaded assignment operator because it's not understanding it. I could be wrong, but if I had to guess, the problem is the combination of trying to link with C source and overloading an operator. I would suggest instead of overloading your assignment operator, that you just create a member function to do the same thing. See if that helps at all.