The first one would appear when using global variables which are shared across files, you just wouldn't see it as the pieces would usually be in separate files.

The first one would appear when using global variables which are shared across files, you just wouldn't see it as the pieces would usually be in separate files. Something like: /* file.h */ int global_i; and you have: /* file.c */ int global_i = 0; Then if file.c includes file.h both will be in the same file during compilation.