Clang Tools

clang-format is a tool that implements automatic source code formatting. It can be used to automatically enforce the layout rules for Sming.

clang-tidy is a C++ “linter” tool to assist with diagnosing and fixing typical programming errors including portability/readability issues, bug-prone code constructs, interface misuse, or bugs that can be deduced via static analysis.

You can find details for the current release at Note that clang-format is part of the main Clang project, whilst clang-tidy can be found in clang-tools-extra.


In Ubuntu you should be able to install them using the following command:

sudo apt-get install clang-format clang-tidy

See the the download page of the Clang project for installation instructions for other operating systems.


Different versions of clang-format can produce different results, despite using the same configuration file.

We are using version 8.0.1 of clang-format on our Continuous Integration (CI) System.

You should install the same version on your development computer.



The coding rules are described in the .clang-format file, located in the root directory of the framework.

You should not edit this file unless it is a discussed and agreed coding style change.

IDE integration

There are multiple existing integrations for IDEs. You can find details in the ClangFormat documentation.

For the Eclipse IDE we recommend installing the CppStyle plugin. You can configure your IDE to auto-format the code on “Save” using the recommended coding style and/or format according to our coding style rules using Ctrl-Shift-F (for formatting of whole file or selection of lines). Read Configure CppStyle for details.

Command Line

Single File

If you want to directly apply the coding standards from the command line you can run the following command:

clang-format -style=file -i Core/<modified-file>

Where Core/<modified-file> should be replaced with the path to the file that you have modified.

All files

The following command will run again the coding standards formatter over all C, C++ and header files inside the Sming/Core, samples and other key directories:

make cs

The command needs time to finish. So be patient. It will go over all files and will try to fix any coding style issues.

If you wish to apply coding style to your own project, add an empty .cs marker file to any directory containing source code or header files. All source/header files in that directory and any sub-directories will be formatted when you run:

make cs

from your project directory.


If you have installed CppStyle as described above you can configure Eclipse to auto-format your files on Save.

Alternatively, you can manually apply the coding style rules by selecting the source code of a C, C++ or header file or a selection in it and run the Format command (usually Ctrl-Shift-F).



No specific version is required but generally you should aim to use the most recent version available in your distribution. Version 17.0.6 was used at time of writing these notes.

The default tool configuration is defined in the .clang-tidy file, located in the root directory of the framework.


Unlike clang-format, clang-tidy has to be able to compile the target code in order to perform static analysis. Code must build without errors for Host architecture.

Clang has more limited constexpr support than GCC so cannot parse some of the FlashString and NanoTime code without modification. However, these changes are only made when __clang__ is defined and do not affect regular builds with GCC.

No object code is generated by clang-tidy.


Only source files which haven’t been built are inspected. So, to restrict which code gets processed built the entire application normally, then ‘clean’ the relevant modules before proceeding with clang-tidy.

For example:

cd $SMING_HOME/../samples/Basic_Servo
make -j SMING_SOC=host
make clean Servo-clean
make CLANG_TIDY=clang-tidy

If you want to fix a particular type of problem, it’s usually best to be explicit:

make CLANG_TIDY="clang-tidy --checks='-*,modernize-use-equals-default' --fix"

Remember to run make cs and check the output before committing!

If you want to provide a custom configuration file:

make CLANG_TIDY="clang-tidy --config-file=myTidyConfig"


clang-tidy can take a long time to do its work, so it’s tempting to use the -j option to speed things up. You may see some corrupted output though as the output from multiple clang-tidy instances aren’t serialised correctly. It’s usually fine to get a rough ‘first-pass’ indication of any problems though.

However, if attempting to apply fixes DO NOT use the -j option as this will result in corrupted output.