Find unused code

I have to refactor a large C# application, and I found a lot of functions that are never used. How can I check for unused code, so I can remove all the unused functions?

Yes, ReSharper does this. Right click on your solution and selection "Find Code Issues". One of the results is "Unused Symbols". This will show you classes, methods, etc., that aren't used.

It's a great question, but be warned that you're treading in dangerous waters here. When you're deleting code you will have to make sure you're compiling and testing often.

One great tool come to mind:

NDepend - this tool is just amazing. It takes a little while to grok, and after the first 10 minutes I think most developers just say "Screw it!" and delete the app. Once you get a good feel for NDepend, it gives you amazing insight to how your apps are coupled. Check it out: http://www.ndepend.com/. Most importantly, this tool will allow you to view methods which do not have any direct callers. It will also show you the inverse, a complete call tree for any method in the assembly (or even between assemblies).

Whatever tool you choose, it's not a task to take lightly. Especially if you're dealing with public methods on library type assemblies, as you may never know when an app is referencing them.

Resharper is good for this like others have stated. Be careful though, these tools don't find you code that is used by reflection, e.g. cannot know if some code is NOT used by reflection.

As pointed Jeff the tool NDepend can help to find unused methods, fields and types.

To elaborate a bit, NDepend proposes to write Code Rule over LINQ Query (CQLinq). Around 200 default code rules are proposed, 3 of them being dedicated to unused/dead code detection

Basically such a rule to detect unused method for example looks like:

// <Name>Dead Methods</Name>
warnif count > 0 
from m in Application.Methods where !m.MethodsCallingMe.Any()
select m

But this rule is naive and will return trivial false positives. There are many situations where a method is never called yet it is not unused (entry point, class constructor, finaliser...) this is why the 3 default rules are more elaborated:

• Potentially dead Types (hence detect unused class, struct, interface, delegate...)
• Potentially dead Methods
• Potentially dead Fields

NDepend integrates in Visual Studio 2017,2015, 2013, 2012, 2010, thus these rules can be checked/browsed/edited right inside the IDE. The tool can also be integrated into your CI process and it can build reports that will show rules violated and culprit code elements. NDepend has also a VS Team Services extension.

If you click these 3 links above toward the source code of these rules, you'll see that the ones concerning types and methods are a bit complex. This is because they detect not only unused types and methods, but also types and methods used only by unused dead types and methods (recursive).

This is static analysis, hence the prefix Potentially in the rule names. If a code element is used only through reflection, these rules might consider it as unused which is not the case.

In addition to using these 3 rules, I'd advise measuring code coverage by tests and striving for having full coverage. Often, you'll see that code that cannot be covered by tests, is actually unused/dead code that can be safely discarded. This is especially useful in complex algorithms where it is not clear if a branch of code is reachable or not.

Disclaimer: I work for NDepend.

I would also mention that using IOC aka Unity may make these assessments misleading. I may have erred but several very important classes that are instantiated via Unity appear to have no instantiation as far as ReSharper can tell. If I followed the ReSharper recommendations I would get hosed!

ReSharper does a great job of finding unused code.

In the VS IDE, you can right click on the definition and choose 'Find All References', although this only works at the solution level.

The truth is that the tool can never give you a 100% certain answer, but coverage tool can give you a pretty good run for the money.

If you count with comprehensive unit test suite, than you can use test coverage tool to see exactly what lines of code were not executed during the test run. You will still need to analyze the code manually: either eliminate what you consider dead code or write test to improve test coverage.

One such tool is NCover, with open source precursor on Sourceforge. Another alternative is PartCover.

Check out this answer on stackoverflow.

I have come across AXTools CODESMART..Try that once. Use code analyzer in reviews section.It will list dead local and global functions along with other issues.

FXCop is a code analyzer... It does much more than find unused code. I used FXCop for a while, and was so lost in its recommendations that I uninstalled it.

I think NDepend looks like a more likely candidate.