Is there a way to identify all the unused global variable in a C project?

Question

I\'m cleaning up some C code. There are global variables everywhere, but not all of them are used. I want to clean up those. But it\'s too much work to test them one by one.

Answer 1

Easy? No. For a global variable X, you need to scan every compilation unit in your code for a potential access to X (a read, a write, or the generation of a reference). If there are no such accesses, then you can be reasonably sure (you don't have any assembly code, right?) that X isn't used.

It may even be the case that X is referenced in one of the above ways, but in fact has no actual effect on the program (e.g., X is read but ignore, written but not read, address taken but never dereferenced). That makes X effectively dead. Determining this requires global data flow analysis.