HelenOS C Coding Style Standard

Any source contribution to HelenOS must follow the C style rules described below.

Source file encoding

• Source files are encoded in UTF-8
• Only ASCII subset should be used, except for cases of internationalized string literals
• New lines are represented by the LF ('\n') character. Do not use CR + LF or CR.

Identifiers

• C identifiers should be written in lower case, words separated by underscore "_" (foo_bar)
• Types shall be suffixed with "_t"
• Preprocesor symbols shall be all-upper case (FOO_MACRO(), FOO_CONSTANT)

Names

• Use sensible, descriptive names.
• Only use English names (English words, intelligible abbreviations)
• Symbols with narrow scope (local variables) may have terse names (e.g. i)
• Symbols with wide scope must have reasonably unique and meaningful names
• Symbols with module scope or wider scope should follow the prefixing convention (e.g. fibril_create)

Indentation

• Use a single Tab character for indentation, except for line continuations.
• Tab width is considered to be 8 characters.
• A line continuation is indented exactly 4 spaces.
• Lines should not, in general, exceed 80 characters (tab counting as 8).
• Each statement shall be placed on a line on its own.
• Braces shall follow ​K&R Bracing Style
  • For functions the opening brace should be at a new line
  • In all other cases the opening brace should be at the same line as the previous token
• Blocks within braces shall be indented 1 tab to the right as compared to the enclosing braces
• Braces without any contents may be placed on the same line.
• Blocks containing a single line can omit braces
  • For if…else statements both or neither of the T, F blocks must be delimited by braces
• Labels in functions and switch statements are not indented (i.e. indented one less tab than the other contents of the block)

Spacing

• All binary arithmetic, bitwise and assignment operators and the ternary conditional operator (? shall be surrounded by spaces
• The comma operator shall be followed by a space but not preceded
• All other operators shall not be used with spaces.
• For functions and function-like operators there should be no extra spaces around or inside parentheses (int foo(void), sizeof(bar_t))
• For control statements with parenteses there should be one space between the keyword and opening parenthesis (if (a == b))
• Return statements should omit parentheses, especially when the argument is simple (return 1;)
• Function-like operators (sizeof()) must never omit parentheses
• There should be no space after asterisk (in type declarations or when dereferencing) (int *foo(int *f), *f = *g[3])

Blank lines

• There should be newline at the end of every source file
• There should be one blank line between any two top-level declarations that include a { } body - functions, enums, structs

Comments

• In general, only /* */ comments are allowed. // comments can be used only to mark transitional code that needs further attention (e.g. // FIXME, // TODO, etc.).
• Comments shall be written in gramatically correct English.
• Comments describing action should be written in infinitive tense (/* Create a new entry on the stack. */)
• Short comments need not be a complete sentence and need not end in '.' Such sentence fragments usually do not contain articles (/* Close callback connection */)
• Multiline comments begin with "*" on each inner line.
• The first line of a multiline comment must be just '/*' and the comment itself must start on the next line ('* Comment…')
• Use Doxygen style comments for documenting functions.
• All comments shall be placed above the line the comment describes, indented identically.
• Every source file, function, type shall have a comment that describes its purpose.
• Bazaar commit comments must follow very similar rules

Miscellaneous

• For vertical spacing (not indentation) spaces instead of tabs should be used (this enables the code to look consistent regardless of the tab size).
• Copyright headers must follow the copyright rules.
• Do not use Yoda comparisons (e.g. NULL == ptr)