Detecting superfluous #includes in C/C++?

Question

I often find that the headers section of a file get larger and larger all the time but it never gets smaller. Throughout the life of a source file classes may have moved and been refactored and it's very possible that there are quite a few #includes that don't need to be there and anymore. Leaving them there only prolong the compile time and adds unnecessary compilation dependencies. Trying to figure out which are still needed can be quite tedious.

Is there some kind of tool that can detect superfluous #include directives and suggest which ones I can safely remove?
Does lint do this maybe?

Answer 1

Here is a simple brute force way of identifying superfluous header includes. It's not perfect but eliminates the "obvious" unnecessary includes. Getting rid of these goes a long way in cleaning up the code.

The scripts can be accessed directly on GitHub.

Answer 2

There's two types of superfluous #include files:

1. A header file actually not needed by the module(.c, .cpp) at all
2. A header file is need by the module but being included more than once, directly, or indirectly.

There's 2 ways in my experience that works well to detecting it:

• gcc -H or cl.exe /showincludes (resolve problem 2)

  In real world, you can export CFLAGS=-H before make, if all the Makefile's not override CFLAGS options. Or as I used, you can create a cc/g++ wrapper to add -H options forcibly to each invoke of $(CC) and $(CXX). and prepend the wrapper's directory to $PATH variable, then your make will all uses you wrapper command instead. Of course your wrapper should invoke the real gcc compiler. This tricks need to change if your Makefile uses gcc directly. instead of $(CC) or $(CXX) or by implied rules.

  You can also compile a single file by tweaking with the command line. But if you want to clean headers for the whole project. You can capture all the output by:

  make clean

  make 2>&1 | tee result.txt

• PC-Lint/FlexeLint(resolve problem both 1 and 2)

  make sure add the +e766 options, this warning is about: unused header files.

  pclint/flint -vf ...

  This will cause pclint output included header files, nested header files will be indented appropriately.

Answer 3

If you are using Eclipse CDT you can try http://includator.com which is free for beta testers (at the time of this writing) and automatically removes superfluous #includes or adds missing ones. For those users who have FlexeLint or PC-Lint and are using Elicpse CDT, http://linticator.com might be an option (also free for beta test). While it uses Lint's analysis, it provides quick-fixes for automatically remove the superfluous #include statements.

Answer 4

This article explains a technique of #include removing by using the parsing of Doxygen. That's just a perl script, so it's quite easy to use.

Answer 5

Gimpel Software's PC Lint can report on when an include file has been included more than once in a compilation unit, but it can't find include files which are not needed in the way you are looking for.

Edit: It can. See itsmatt's answer

Answer 6

Google's cppclean (links to: download, documentation) can find several categories of C++ problems, and it can now find superfluous #includes.

There's also a Clang-based tool, include-what-you-use, that can do this. include-what-you-use can even suggest forward declarations (so you don't have to #include so much) and optionally clean up your #includes for you.

Current versions of Eclipse CDT also have this functionality built in: going under the Source menu and clicking Organize Includes will alphabetize your #include's, add any headers that Eclipse thinks you're using without directly including them, and comments out any headers that it doesn't think you need. This feature isn't 100% reliable, however.