[Discuss] finding dead code in C projects

[bogstad at pobox.com (Bill Bogstad)]

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On Mon, Jun 17, 2013 at 5:03 PM, Greg Rundlett (freephile)
<greg at freephile.com> wrote:
> I'm wondering if anyone has success stories about finding dead code in
> large (C) projects?

I'm not sure I can provide any help with this question, but I think it
would help if you defined
what you mean by dead code.   Some possible definitions:

1. Functions which are defined but there is no static call site in the
code base.

1a. Like 1, but with all possible definitions of various C
preprocessor definitions.  Not just the ones for your current build
environment.

2. What about conditional statements that will always be true/false
statically OR for any real runtime enviroment. Is the alternative
branch of the conditional dead code?

3. What about functions that are assigned to (arrays/structs of)
function pointers?   You can't really tell until runtime if those
functions will ever be called.   Kind of like #2...

BTW, I took a quick look at
http://www.samba.org/ftp/unpacked/junkcode/findstatic.pl and it
appears to handle case #1, but not 1a.

As Tom suggests, this is related to comprehensive unit tests; but
determining if your unit tests
are complete is not always easy and may be difficult to do.   For
example, injecting errors
into system calls in order to test error recovery can be difficult to
accomplish.  Getting fork() to fail could be a challenge.

In the end, I think your goal is related to the halting problem which
is impossible in the general case.  So use the tools, you are
comfortable with and accept that you probably won't find everything.

Bill Bogstad