C Code and General Style Guidelines

Coding style is enforced on any new or modified code, but contributors are not expected to correct the style on existing code that they are not modifying.

For style aspects where the guidelines don’t offer explicit guidance or permit multiple valid ways to express something, contributors should follow the style of existing code in the tree, with higher importance given to “nearby” code (first look at the function, then the same file, then subsystem, etc).

In general, follow the Linux kernel coding style, with the following exceptions and clarifications:

  • Use snake case for code and variables.

  • The line length is 100 columns or fewer. In the documentation, longer lines for URL references are an allowed exception.

  • Add braces to every if, else, do, while, for and switch body, even for single-line code blocks.

  • Use spaces instead of tabs to align comments after declarations, as needed.

  • Use C89-style single line comments, /*  */. The C99-style single line comment, //, is not allowed.

  • Use /**  */ for doxygen comments that need to appear in the documentation.

  • Avoid using binary literals (constants starting with 0b).

  • Avoid using non-ASCII symbols in code, unless it significantly improves clarity, avoid emojis in any case.

  • Use proper capitalization of nouns in code comments (e.g. UART and not uart, CMake and not cmake).