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

Header:

extern const char    *Bittorrent;

Main (before the main function / as gloabal variable):

const char    *Bittorrent     =   "BitTorrent protocol";

This way your header tells every file that there is variable named "Bittorrent", but only your main.c file has the part in it where it is really created.