Problems compiling two c programs together

setup.c has the global variable login. How come this isn't variable visible in main.c? Here is the code and output that I get.

Code:

$ more setup.c
#include <pwd.h>
#include <string.h>
/*#include "me.h"*/

#define MAXLOGIN 64

char login[MAXLOGIN];

void init(void)
{
  struct passwd *pwd;

  if ((pwd = getpwuid(geteuid())) == NULL)
    strcpy(login, "unknown");
  else
    strcpy(login, pwd->pw_name);
}

Code:

$ more main.c
/*I gave up trying to read Dr. Thalers code*/

#include <stdio.h>
#include <stdlib.h>
/*#include "me.h"*/

int main(int argc, char *argv[]) 
{

  /*begin the clownsuit and bra masturbation session*/
  init();

  printf("%s\n", login);
  exit(EXIT_SUCCESS);
}

$ gcc -g setup.c main.c -o yapp
main.c: In function ‘main’:
main.c:13: error: ‘login’ undeclared (first use in this function)
main.c:13: error: (Each undeclared identifier is reported only once
main.c:13: error: for each function it appears in.)

Use

Code:

extern char login[MAXLOGIN];

in main.c.

I don't think you need to specify the size.

Originally Posted by Brafil

I don't think you need to specify the size.

No, the extern declaration doesn't have to have a size. But as long as it is a constant declared in one place, why not make it obvious what the size is, rather than leaving it empty to then have to find the original definition of the variable to see what the actual size is. Obviously, it would be a bad idea to put a constant "magic" number in there, e.g. 100 - because it's hard to do that.

--
Mats

Just in case the size might change and someone forgets this file... well, it really doesn't matter.

Originally Posted by Brafil

Just in case the size might change and someone forgets this file... well, it really doesn't matter.

That's why I said, phrazed slightly differently, something lie "as long as it's not a magic number, but a #define or const definition, it's fine" - obviously also assuming that the constant is defined in a single header-file that is included in both places, of course.

--
Mats

Yes, that's what I assumed.