[SOLVED] Redefinition error while accessing a global variable defined in executable from library

Issue

I have static library file(lib_XXX.a) with global variable defined in it. I am trying to access the global variable in my executable(exe_XXX.o). Linker error is coming. Any help would be thankful.

Languae : c
OS : Ubuntu gcc compiler

Sample as follows

exe_xxx.o module has 2 files resource.h and main.c

resource.h code as follows :

#ifndef RESOURCE_H
#define RESOURCE_H

#define APL

extern const StructTest g_AplObjDef;

const StructTest g_AplObjDef = {
abc, def, ghi,
....
};

#endif //APL

main.c code as follows:

#include "resource.h"
....
....
....

lib_xxx.a has another main.c in it. Its sample code as follows:

#include "resource.h"

int main()
{
#if defined(APL)
     fun1(g_AplObjDef);
#endif
}

I suspect the reason is because resource.h included in both the main.c files. I couldn't way to get rid of this. Can anyone help ?

Error details: /lib_XXX.a(lib_XXX_a-main.o):(.data.rel.ro.local+0x40): `g_AplObjDef' が重複して定義されています /exe_xxx-main.o:(.data.rel.ro.local+0x260): ここで最初に定義されています

Above error is in Japanese.. 1st line says "Duplicate is defined". 2nd line says "Here it is defined"

Solution

This part:

const StructTest g_AplObjDef = {
    abc, def, ghi,
    ....
};

is a definition, and should not be in a header. Move it to a .c file.

The reason for this is that header files are textually inserted, so if a header has a definition, and is included from multiple translation units, the symbol will be defined multiple times, which is an error.

Answered By - sp2danny