To sort out messy header files, I use include what you use

Abstract ： Use include-what-you-use(iwyu/IWYU) Clean up redundant header files , Add necessary header files .

This article is shared from Huawei cloud community 《​ ​ use include what you use Save the chaotic header file ​​》, author ： Under the village tree .

background

Face large C/C++ When the project is , Confusing header file references , There is often a feeling of being cut and disordered . Years of project iterations , Demand update . As a result, the header file is not updated in time with the code changes , Become a burden of redundancy . This will increase the compilation time of the overall project . If I don't have a tool to help me organize these header files , I will never change their mind . Fortunately, , There is a tool that can meet our requirements –include what you use.

brief introduction

In all kinds of C/C++ In the coding specification , There are usually a few points mentioned ：

Do not include unused header files

Unused header files are included at the same time , Introduced unnecessary dependencies , Increased coupling between modules , As long as the header file is modified , The code will be recompiled .

The header file should contain itself

If a file contains a header file . Want to work properly , You must also include another header file , This will increase the burden of use .

So this is also the meaning of sorting header files . This is also used include-what-you-use（ Hereinafter referred to as IWYU） The purpose of .

install

Attach the home page for this project
​ ​https://github.com/include-what-you-use/include-what-you-use​​IWYU rely on Clang, And it targets Clang Each version of has its own version . So in installation IWYU When , First you need to determine your Clang What version is it . Because I have not installed Clang, So first install Clang.

Clang Installation

It is recommended to compile the source code directly , Reduce strange errors such as symbol incompatibility
clone llvm Warehouse

git clone ​ ​https://github.com/llvm/llvm-project.git​​

Switch to the one you want to compile llvm edition

cd llvm-project
git checkout llvmorg-14.0.0

structure LLVM and Clang

cd llvm-project
mkdir build && cd build
cmake -DLLVM_ENABLE_PROJECTS=clang -DCMAKE_BUILD_TYPE=Release -G “Unix Makefiles” …/llvm
make -j48

IWYU install

clone IWYU Warehouse

git clone ​ ​https://github.com/include-what-you-use/include-what-you-use.git​​cd include-what-you-use

Switch to and clang Corresponding branch , Because what was just installed 14.0 Version of , So here we also switch to the corresponding version

git checkeout clang_14

stay IWYU Create folders one level above build

mkdir build && cd build
cmake -G “Unix Makefiles” -DCMAKE_PREFIX_PATH=…/llvm/llvm-project/llvm/ …/include-what-you-use/

CMAKE_PREFIX_PATH Point to the just built llvm Catalog . If the build is successful , You'll see

Start compilation IWYU

cd …/include-what-you-use/
make -j48

Compile successfully

If you want more convenient use iwyu, It can be bin Add environment variables , I am creating a soft link to /usr/bin Under the table of contents

ln -s /the/path/of/include-what-you-use/bin/include-what-you-use /usr/bin/iwyu

If all is well , You can use it iwyu -v To check whether the installation was successful

Use

Here is an introduction to Clion In the environment , How to use IWYU
open Clion->File->Setting->Build,Execution,Deployment page

• Set up compiler
  In the official documentation , Introduce use IWYU When , Use Clang As a compiler . Discover through personal practice , stay 14.0 Under the version ,Gcc 7.3.1 It can also be used IWYU Of .
  stay Toolchains Set in Clang The path of , Because of me Gcc It can also run , So there is no change
  
• Set compilation options
  ->Cmake Setup page .
  Create a new compilation template named Debug-iwyu, The focus is on Cmake options Add  -DCMAKE_CXX_INCLUDE_WHAT_YOU_USE=iwyux  among iwyu Be practical in your environment include-what-you-use Path to executable file
  
• Compile the project
  Select the newly created compilation template in the compile project interface Debug-iwyu
  
  OK, Everything is all set. , You can start compiling .
• The result processing
  Here is a very simple example ,main.cpp Contains three unused header files
  
  then iwyu During compilation, we will be reminded that these three header files should be removed
  
  But in real large projects , There must be a lot of reminders , Manually modify one by one . Still a mechanical coolie , So in iwyu In the project , Provides a script that can assist in automatic repair fix_includes.py. You can refer to the usage of the project homepage , To help automatically repair .
• [1]​ ​IWYU Home page ​​
• [2] Clang Build guidance

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