global var problems

Hello, I've come across an interesting problem I haven't had before.

Here is an example:

I have a variable called testVar which should be available to any .c file that #includes test.h. For some reason though I receive this error:

/tmp/ccKsh4uo.o: In function `myFunction':
test.c: (.text+0x5): undefined reference to `testVar'
collect2: ld returned 1 exit status

Here is my code:

Code:

// File: test.h

extern char testVar;

Code:

// File: test.c

#include <stdio.h>
#include "test.h"

void myFunction()
{
        testVar = 'b';
}

int main()
{
        char testVar = 'a';

        myFunction();

        printf("%c", testVar);

        return 0;
}

Any ideas why this would happen?

did you compile test.o as a separate object (gcc -c if you're using gcc)? otherwise your compiler expects some source to contain the effective definition of testVar (the global one).

Originally Posted by root4

did you compile test.o as a separate object (gcc -c if you're using gcc)? otherwise your compiler expects some source to contain the effective definition of testVar (the global one).

I'm using:

root@c64:/root/testarea# gcc test.c test.h

and where is defined testVar? it's not defined in test.c, so as expected your compiler does not agree.

Originally Posted by root4

and where is defined testVar? it's not defined in test.c, so as expected your compiler does not agree.

testVar is defined in test.c in the main() function as indicated above

char testVar = 'a';

test.h _declares_ a _global_ variable named testVar, defined nowhere in your code
The testVar='a' you're speaking about is a _local_ variable defined in main(), not related at all to the other one...
plus myfunction() uses obviously the global one, so check what you really want to do and fix it. Don't name local and global variables identically, despite this is authorized, it leads to misunderstandings like this one.

And don't compile header files; only source files.