How to enable checking of unused includes ?

fernandesh

Dear all,

qtCreator is a great tool, but I am missing some features that are natively enabled in IDEs specialized in Java or Python.

For instance, in the code below, obviously the header thread is not used, but I couldn't enable this warning.

#include <iostream>
#include <thread>

int main()
{
    std::cout << "Hello World!" << std::endl;
    return 0;
}

In longer codes that warning can be useful.

JonB

@fernandesh
It will be interesting to see if the C++ experts know better, but I don't think this could be done for C++. #include files can contain all sorts of stuff, and preprocessor directives, I would have thought it would be very difficult to be sure that nothing in an included had any effect anywhere. Java or Python are more organized/restrictive on imports. I do not recall seeing any IDE for C++ showing me included files were not needed.

Now someone will tell me I'm quite wrong.... :)

Christian Ehrlicher

@JonB You're correct.
There are some external tools like e.g. https://github.com/include-what-you-use/include-what-you-use

fernandesh

@JonB, thanks for your enlightening answer.

What you pointed was one of my concerns, too: for instance, defines can be anywhere.

However, in a world of precompiled headers, maybe there's light to this possible (and sometimes probable) mess.

And someday the C++ modules (defined in C++20) will become a reality and we C++ programmers will no longer be envious of Python and Java.

JoeCFD

@JonB Qt Creator 12 has this feature now. It highlights unused includes, but not all of them are correct.

JonB

@JoeCFD said in How to enable checking of unused includes ?:

but not all of them are correct.

Which is my point! I would have thought it might give false positives (in the sense of thinking an include had no effect when it actually does). Might be pathological cases, I don't know.

fernandesh

Thanks for your reference @Christian-Ehrlicher !

include-what-you-want looks promising, and is project constantly updated. I'll give it a try.

JoeCFD

@JonB But good enough. Very easy to test. Nice feature.

Chris Kawa

It mostly depends on how close to the compiler is the editor's code model. Those have to take some shortcuts for the sake of speed, but they are getting pretty good.

I don't know about Qt Creator, but I've used it in Visual Studio and Rider and both work pretty much as expected. The few false positives are usually a simple compilation error because of a missing type, so an easy fix. Of course you can always f up your project if you use a bunch of conditionals in the preprocessor, but that's always a risk even without the feature.

aha_1980

As @Chris-Kawa and @JoeCFD already said, Creator now has this feature.

It is provided by Clangd, and therefore as good as Clangd understands your project.

In header files, I got some false positives also, but in source files it works quite good.

Regards