Finding “dead code” in a large C++ legacy application [closed]

Answer 1

One approach is to use "Find All References" context menu item on class and function names. If a class/function is only referenced in itself, it is almost certainly dead code.

Another approach, based on the same idea, is to remove(comment out) files/functions from project and see what error messages you will get.

Answer 2

See our SD C++ Test Coverage.

You need to do a lot of dynamic testing to exercise the code, to make sure you hit the maximum amount of coverage. Code "not covered" may or may not be dead; perhaps you simply didn't have a test case to exercise it.

Answer 3

Although not specifically for dead code, I found the Source Navigator

http://sourcenav.berlios.de/

quite useful, although cumbersome to set up and a bit buggy. That was a year ago on Linux (Fedora).

Answer 4

You'll want to use a static analysis tool

• StackOverflow: What open source C++ static analysis tools are available?
• StackOverflow: C++ static code analysis tool on Windows
• Wikipedia: List of tools for static code analysis

The main gotcha I've run into is that you have to be careful that any libraries aren't used from somewhere that you don't control/have. If you delete a function from a class that gets used by referencing a library in your project you can break something that you didn't know used the code.

Answer 5

Nothing beats familiarity with the code. Except perhaps rigourous pruning as one goes along.

Sometimes what looks like deadwood is used as scaffolding for unit tests etc, or it appears to be alive simply because legacy unit tests exercise it, but it is never exercised outside of the tests. A short while ago I removed over 1000 LOC which was supporting external CAD model translators, we had tests invoking those external translators but those translators had been unsupported for 8+ years and there was no way that a user of the application even if they wanted to could ever invoke them.

Unless one is rigourous in getting rid of the dead wood, one will find your team maintaining the stuff for years.

Answer 6

You can use Cppcheck for this purpose:

$ cppcheck --enable=unusedFunction .
Checking 2380153.c...
1/2 files checked 0% done
Checking main.c...
2/2 files checked 0% done
[2380153.c:1]: (style) The function '2380153' is never used.