Global arrays shared between multiple source files

[mike_g]

I have a couple of global arrays that I want to be accessible in a few source files, but I cant get it to work. First I tried using a shared header:

#ifndef HEADER_SEEN
	#define HEADER_SEEN 
        //In here
#endif

Which seems to work for my #defines and struct definitions, but if I put the arrays in there gcc moans about multiple definitions.

If I put the code in main then the other source files cant see it. I dont know if this makes a difference but I am assigning values to the arrays as I declare them.

How can I fix this?

Cheers.

[zacs7]

Tell the linker they exist elsewhere...

globals.h

#ifndef INCLUDED_GLOBALS_H
#define INCLUDED_GLOBALS_H

extern int myVar;

#endif /* INCLUDED_GLOBALS_H */

main.c

#include "globals.h"
#include "something.h"

int myVar = 10;

int main(void)
{
    printf("myVar = %d\n", myVar);
    something_whatever();
    printf("myVar = %d\n", myVar);

    return 0;
}

something.c

#include "globals.h"

void something_whatever(void)
{
    myVar = 50;
}

You could also add set/fetch methods in main.c and call them from something.c (that way you can control how and who can set it). Otherwise it's a tad "dangerous"

[mike_g]

THanks zacs, that seems to work, but I dont seem to be able to initialise them as they are declared. Is there any way that I can do this?

[zacs7]

Why not? Remember it's declared in main.c:

main.c

char myArray[128] = "Initial value";

void main(void)
{
    /* ... */

globals.h

#ifndef INCLUDED_GLOBALS_H
#define INCLUDED_GLOBALS_H

extern char myArray[128];

#endif /* INCLUDED_GLOBALS_H */

[mike_g]

Oh, I found what was wrong; I had them declared as const datatypes.

Cheers.