Why does global variables in a header file cause link error?

Question

I always get the following error, even if I have put include guard in header file.

duplicate symbol _Bittorrent in:
    /Users/tracking/Library/Developer/Xco         


        

Answer 1

By initializing the variable, you are defining it in every place that the file is included. Assuming that these modules are linked together, you now have multiple definitions, which is an error.

You can declare the variable in your header with an extern tag and then initialize it in one of your .c modules.

In your .h file:

extern int i;

In one of your .c files:

int i = 1;

However,