Global struct problems with VBCC

[Csoft]

Hello all,

I'm facing a weird problem with vbcc. I want to have a global struct on my project. I extracted the problem here.

struct.h

struct {

    int a;

    int b;

} myStruct;



void change();

________________________________________

struct.c

#include "struct.h"



void change() {

    myStruct.a = 40;

}

________________________________________

main.c

#include <stdio.h>

#include "struct.h"



int main () {

    myStruct.a = 10;

    change();

    printf ("%d\n",myStruct.a);

}

________________________________________

Makefile

gcc:

	gcc	struct.c main.c -o main.exe



vbcc:

	vc +kick13 struct.c main.c -o amigamain.exe

________________________________________


Everything compiles and run with gcc on linux, but when I try to compile this with vbcc targeting amiga this error happens:

Error 19: /var/tmp/tmp.1.o: Global symbol _myStruct from tmp.1.o is already defined in tmp.0.o.

I cannot understand why! Have any idea?

Thank you in advance.

[Asman]

@Csoft

Change struct.h to

#ifndef PROJECT_STRUCT_H
#define PROJECT_STRUCT_H

struct {

    int a;

    int b;

} myStruct;



void change();

#endif /*PROJECT_STRUCT_H*/

[Steady]

You are actually creating a myStruct variable in the header file which then is included in both c files. This causes your error.

Define in the .h file:

struct myStruct
{
int a;
int b;
};



If you want it to be global, in ONE of your .c files add:
struct myStruct myStruct;

In the other .c file, add:
extern struct myStruct myStruct;


It would be better not to use a global across .c files if you can help it, and just pass a pointer to myStruct in to the called functions as needed. Also, it would be better to use a different name from the actual structure type. (i.e. don't call both the structure and variable myStruct).

[Csoft]

Thank you guys!!! I solved!!!

Yes, I know that global variables are usually considered bad, but in my scenario there's a reason, I can always change my mind.

Thanks again!

[phx]

Steady is right. vbccm68k behaves like all classic Amiga compilers here, because Common symbols were never really supported in hunk-format object files (partly starting with V36?). So gcc is (as usual) special here, because it uses Common symbols for mystruct.

A Common symbol is allowed to be defined in multiple objects with the same name, and the linker will merge them into a common address space, using the size of the largest definition.

You can get the same with vbcc when using the option -use-commons.