Accessing a static variable of one compilation unit from others directly, in C

Question

So I'm working on a "quick and dirty" profiler for firmware- I just need to know how long some functions take. Merely printing the time it takes every time will skew the results, as logging is expensive- so I am saving a bunch of results to an array and dumping that after some time.

When working in one compilation unit (one source file), I just had a bunch of static arrays storing the results. Now I need to do this across several files. I could "copy paste" the code, but that would be just ugly (Bear with me). If I put timing code in a seperate compilation unit, make static variables, and provide accessor functions in the header file, I will be incurring the overhead of function calls every time i want to access those static variables.

Is it possible to access static variables of a compilation unit directly?

I've always tried to encapsulate data, and not use global variables, but this situation calls for it simply due to speed concerns.

I hope this makes sense! Thank you!

EDIT: Alright, so it appears what I'm asking is impossible- do any of you see alternatives that essentially allow me to directly access data of another compilation unit?

EDIT2: Thank you for the answers Pablo and Jonathan. I ended up accepting Pablo's because I didn't have clear place to get the pointer to the static data (as per Jonathan) in my situation. Thanks again!

Answer 1

No, it's not possible to access static variables of a compilation unit from another one. static keyword precisely prevents that from happening.

If you need to access globals of one compilation unit from another, you can do:

file1.c:

int var_from_file1 = 10;

file2.c:

extern int var_from_file1;
// you can access var_from_file1 here

If you can remove the static keyword from your declarations, you should be fine. I understand that changing existing source code is not always an option (I.E. dealing with existing legacy compiled code).

Answer 2

To get at the static variables in a compilation unit C1 from another unit C2, some function in C1 must make pointers to the variables available to C2, or some non-static variable must contain a pointer to the static variables.

So, you could package the 'static variables' into a single structure, and then write a function that returns a pointer to that structure; you can call that function to gain access to the static variables.

Similar rules apply to static functions; if some function (or non-static variable) in the file makes the pointers to the functions available, then the static functions can be called indirectly from outside the file.

If access via pointers doesn't count as directly, then you are snookered; static hides and you can't unhide except by removing the keyword static from the variables when the module is compiled - maybe via the C preprocessor. Beware name clashes.