Dead code detection in legacy C/C++ project
How would you go about dead code detection in C/C++ code? I have a pretty large code base to work with and at least 10-15% is dead code. Is there any Unix based tool to identify this areas? Some pieces of code still use a lot of preprocessor, can automated process handle that?
Answer
You could use a code coverage analysis tool for this and look for unused spots in your code.
A popular tool for the gcc toolchain is gcov, together with the graphical frontend lcov (http://ltp.sourceforge.net/coverage/lcov.php).
If you use gcc, you can compile with gcov support, which is enabled by the '--coverage' flag. Next, run your application or run your test suite with this gcov enabled build.
Basically gcc will emit some extra files during compilation and the application will also emit some coverage data while running. You have to collect all of these (.gcdo and .gcda files). I'm not going in full detail here, but you probably need to set two environment variables to collect the coverage data in a sane way: GCOV_PREFIX and GCOV_PREFIX_STRIP...
After the run, you can put all the coverage data together and run it through the lcov toolsuite. Merging of all the coverage files from different test runs is also possible, albeit a bit involved.
Anyhow, you end up with a nice set of webpages showing some coverage information, pointing out the pieces of code that have no coverage and hence, were not used.
Off course, you need to double check if the portions of code are not used in any situation and a lot depends on how good your tests exercise the codebase. But at least, this will give an idea about possible dead-code candidates...