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How to avoid multiple definition of a variable by multiple inclusion of a header file

Easily described problem:

Using g++ version 3.3.5 under suse 9.3,

#ifndef myTEST
#define myTEST
ZFSInt test;

leads to an error at link time...
application.o(. bss+0x0):/path_here/application.cpp :19: multiple
definition of `test'
app.o(.bss+0x0) :/path_here/app.cpp:17: first defined here
....for EVERY call of #include "bla.h"

Apparently the #ifndef only works at compile time, but somehow causes
an error at linktime. Any solution? I want the variable "test"
available in all modules that #include "bla.h"


Lars Uffmann

Aug 1 '06
11 22596

In my implementation, it is like

#ifndef TEST
#define TEST
const char* strDescriptions[] = {"Desc1", "Desc2", "Desc3"};

How to split the definition and definition of the above.

Chinthan EP
la**********@rw th-aachen.de wrote:
Mi************* @tomtom.com schrieb:
This has nothing to do with #ifdef, which is a preprocessor command.
It works only at compile time, and skips every second defintion of 'test'
*in a single .cpp*, not across .cpp's. As the compiler works on single
.cpp's it won't notice that.

Woohoo - I see light in the dark! Finally the explanation I've been
waiting for :) To be honest, I suspected something like this, because
the compiler creates libraries for each cpp file separately, so the
linker would spot multiple declarations of the variable, but in that
case the sense of the preprocessor commands did not occur to me - I
never realized it was only to skip further definitions within the same

Thanks for clearing this up! :)
And to all the others that helped solving the problem!


Aug 5 '06 #11
ch********@gmai l.com wrote:

In my implementation, it is like

#ifndef TEST
#define TEST
const char* strDescriptions[] = {"Desc1", "Desc2", "Desc3"};

How to split the definition and definition of the above.
First, please don't top-post on Usenet, your reply belongs below or
interleaved with the post you are replying to.

to split, declare the variable in a header and define in once and once
only in a source module.

In test.h:

extern const char* strDescriptions[];

in somefile.cc:

const char* strDescriptions[] = {"Desc1", "Desc2", "Desc3"};

Ian Collins.
Aug 5 '06 #12

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