Re: Easy Question - LINK2005 error

From:

David Wilkinson <no-reply@effisols.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Thu, 05 Jul 2007 16:11:56 -0500

Message-ID:

<uYt#4C0vHHA.4228@TK2MSFTNGP06.phx.gbl>

bones288 wrote:

////////// main.cpp //////////

#include <iostream>
#include "try.cpp"
using namespace std;

int main()
{
Num Try;
return 0;
}

//////// try.cpp //////////
#include <iostream>

class Num{
private:
int number;
public:
void SetNumber(int);
};

void SetNumber(int a)
{
}

///////////OUTPUT GENERATED//////////
------ Rebuild All started: Project: try_examples, Configuration:
Debug Win32 ------
Deleting intermediate and output files for project 'try_examples',
configuration 'Debug|Win32'
Compiling...
try.cpp
try_example.cpp
.\main.cpp(9) : warning C4101: 'Try' : unreferenced local variable
Generating Code...
Linking...
try.obj : error LNK2005: "void __cdecl SetNumber(int)" (?
SetNumber@@YAXH@Z) already defined in try_example.obj
try.obj : error LNK2005: "void __cdecl SetNumber(int)" (?SetNumber@@$
$FYAXH@Z) already defined in try_example.obj

try_examples - 3 error(s), 1 warning(s)
========== Rebuild All: 0 succeeded, 1 failed, 0 skipped ==========

bones:

Because Try.cpp has the.cpp extension it is being compiled as a
translation unit. The translation unit generated by main.cpp includes
Try.cpp, so your function SetNumber() is defined in both translation
units. Rename Try.cpp to (say) Try.h and this error will go away.

But there are a lot of other things wrong also.

1. I'm sure you meant

void Num::SetNumber(int a)
{
number = a;
}

2. When you define a class method in an include file, you must either
define it inside the class definition (implicit inline) or use the
inline qualifier

inline void Num::SetNumber(int a)
{
number = a;
}

Otherwise if you include it in more than one .cpp file you will get
multiple definition errors again.

3. Your Try.cpp does not use iostream, so it should not include <iostream>

--
David Wilkinson
Visual C++ MVP