link error.

[Kiran Pinjala]

i have a

CSocket SomeSocket;

variable declared globally in a "one.h" file.I have inlcuded this one.h in one.cpp as

#include "one.h"

I used this SomeSocket in another two.h files where i have included the file

#include "one.h"

now i get a linker error stating

two.obj : error LNK2005: "CSocket SomeSocket" (?xst@@3UGlobals@@A)
already defined in one.obj

what was the mistake. -- modified at 6:54 Friday 30th November, 2007

Adi Vishayam

[Cedric Moonen]

You need to put include guards in your header file: #ifndef YOURFILE #define YOURFILE // Code here #endif (replace YOURFILE by something unique, like the file name). You could also use #pragma once for microsoft compiler.

---

Cédric Moonen Software developer
Charting control [v1.2]

[Kiran Pinjala]

Cedric Moonen wrote:

You could also use #pragma once for microsoft compiler

#pragama once is already added. problem remains the same.

Adi Vishayam

[CPallini]

you have to declare it extern inside your include file (i.e. "one.h")

extern CSocket SomeSocket;

and then define once inside a single source file (e.g. in your "one.cpp").

CSocket SomeSocket;

The mistake is in your include file: as it stands CSocket SomeSocket is defined in multiple source files. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.

[Iain Clarke Warrior Programmer]

CPallini has given you the correct answer. But I see this mistake a lot with novice programmers. The linker is complaining because (as it says) you have two instances of SomeSocket. Before the compiler attacks you "one.c" file, a preprocessor attacks it, and processes the includes. An easy exercise for you: remove the #include from one.c, and cut and paste the whole of one.h into the top of one.c. Do this for two.c. Now have a lightbulb moment as you realise what the linker is telling you. Iain.