This is a modification of the style guide provided by [].

File Layout

  • Comment with LICENSE
  • Headers
  • Macros
  • Types
  • Function declarations
    • Include variable names
    • For short files these can be left out
    • Group/order in logical manner
  • Global variables
  • Function definitions in same order as declarations
  • main

C Features

  • Up to C99 without extensions
  • POSIX.1-2008
  • Declarations should not be mixed with statements
  • Loop initial declarations should not used
  • C style /* */ comments should be used, not C++ style // comments
  • #if 0 #endif must be used to comment out code, not /* */
  • Variadic functions and macros are acceptable, but require safety


  • { on same line preceded by single space (except functions)

  • } on own line unless continuing statement (e.g. if else)

  • Blocks are used for single statements if and only if

    • An inner statement needs a block:

      for (;;) {
          if (foo) {
    • Another branch of the same statement needs a block:

      if (foo) {
      } else {
    • One exception to this rule is nested for loops like below:

      for (i = 0; i < 64; ++i)
      for (j = 0; j < 32; ++j)
      for (k = 0; k < 16; ++k) {
          /* ... do stuff here ... */

Indentation and Line Length

  • The maximum line length is 80 columns
  • Tabs are used for indentation with a visual width 8-spaces
  • An extra indent or two should be used when wrapping lines
  • String literals used in error messages are an exception to these rules:
    • This makes them easy to search for with grep
  • Multiline string literals should be continued with \


  • Modifiers and the return type on their own line
  • Function name and argument list on the next line
  • Opening { must be on its own line (functions are special)
  • Functions not used outside translation unit must be static


  • Should be declared as close as possible to initialization/use

  • Global variables not used outside translation unit should be static

  • In declaration of pointers the * must be touching the variable name, not the type:

    int *foo;


  • Space after if, for, while, and switch as these are not function calls
  • Space should not be used after the opening ( and before the closing )
  • Parentheses must be used with sizeof
  • sizeof() must be written as a function call since it acts like one
  • switch statements and their cases share the same indentation level
  • switch cases that FALLTHROUGH should be commented


  • Include libc/system headers come first alphabetically
    • If order cannot be alphabetical, a comment must explain
  • There must be a blank line between system headers and project headers
  • When writing and using local headers
    • Include guards must be used
    • Should be included alphabetically

User Defined Types

  • Typedef is not used for structs which have fields meant to be accessed
  • Typedef is allowed for opaque types, enums, and error codes
  • Type names should be all lowercase

Handling Errors

  • Use Linux style gotos in a function that can fail and must cleanup multiple resources before exiting

  • Errors or failures should be returned from early rather than later in nested code:

    • Like so:

      if (err)
    • Instead of:

      if (success) {
          /* Do stuff */
      } else {

Enums vs #define

  • Use enums for values that are grouped semantically and #define otherwise:

    #define MAXSZ  4096
    #define MAGIC1 0xdeadbeef
    enum {