Declaring,initializing and using a global variable in same header file

Question

I am actually trying to use a variable that is initialized in a header file(say x.h) and want to use same variable inside inlined code in the same header file. The same var

Answer 1

Using the extern reserved word.

Never create variables in '.h' files, it's a bad practice that leads to bugs. Instead, declare them as extern everywhere you need to use them and declare the variable itself only in a single '.c' file where it will be instantiated, and linked to from all the other places you use it.

Answer 2

You can declare the global variable in the header file as extern, and then define it inside a code-module (i.e., ".c" file). That way you won't end up with multiple definition errors thrown by the linker.

So for example in your header file, a globally available int named my_global_var would have a declaration in a .h file that looks like:

extern int my_global_var;

Then inside a single .c file somewhere you would define and initialize it:

int my_global_var = 0;

Now you can use my_global_var in any other code module that includes the appropriate header file and links with the proper .c file containing the definition of the global variable.