Declaring a global variable in C with .mm and .h files?

Hello computing peoples of the world!

I have a bunch of .mm with their respective .h files. I would like one global unsigned int variable that I could use throughout all the source files. Right now I'm trying to do this by开发者_如何学C placing this statement in one of the .h files:

 extern unsigned int global_size_of_instrumental;

But I'm getting super strange errors such as:

Any ideas?

extern is an indicator that the variable is defined somewhere else rather than "here".

Somewhere (preferably in a C file to avoid the possibility of multiple definitions), you will need just:

unsigned int global_size_of_instrumental;

You need to put this in only one of the .mm files:

unsigned int global_size_of_instrumental;

And then, in every other .mm you need to use (reference) it put:

extern unsigned int global_size_of_instrumental;

Done.