Recommended Reading

• OpenBSD style(9)
• Pike style
• Linux kernel coding standards

File Layout

• Comment with LICENSE and possibly short explanation of file/tool.
• 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

• Use C99 without extensions (ISO/IEC 9899:1999).
• Use POSIX.1-2008:
• When using gcc define _POSIX_C_SOURCE 200809L.
• Alternatively define _XOPEN_SOURCE 700.
• Do not mix declarations and code.
• Do not use for loop initial declarations.
• Use /* */ for comments, not //.
• Variadic macros are acceptable, but remember:
• __VA_ARGS__ not a named parameter.
• Arg list cannot be empty.

Blocks

• All variable declarations at top of block.
• { on same line preceded by single space (except functions).
• } on own line unless continuing statement (if else, do while, ...).

Use block for single statement if inner statement needs a block.

for (;;) {
	if (foo) {
		bar;
		baz;
	}
}

Use block if another branch of the same statement needs a block:

if (foo) {
	bar;
} else {
	baz;
	qux;
}

Leading Whitespace

Use tabs for indentation and spaces for alignment. This ensures everything will line up independent of tab size. This means:

• No tabs except beginning of line.
• Use spaces - not tabs - for multiline macros as the indentation level is 0, where the #define began.

Functions

• Return type and modifiers on own line.
• Function name and argument list on next line. This allows to grep for function names simply using grep ^functionname(.
• Opening { on own line (function definitions are a special case of blocks as they cannot be nested).
• Functions not used outside translation unit should be declared and defined static.

Example:

static void
usage(void)
{
	eprintf("usage: %s [file ...]\n", argv0);
}

Variables

• Global variables not used outside translation unit should be declared static.
• In declaration of pointers the * is adjacent to variable name, not type.

Keywords

• Use a space after if, for, while, switch (they are not function calls).
• Do not use a space after the opening ( and before the closing ).
• Preferably use () with sizeof.
• Do not use a space with sizeof().

Switch

• Do not indent cases another level.
• Comment cases that FALLTHROUGH.

Example:

switch (value) {
case 0: /* FALLTHROUGH */
case 1:
case 2:
	break;
default:
	break;
}

Headers

• Place system/libc headers first in alphabetical order.
• If headers must be included in a specific order add a comment to explain.
• Place local headers after an empty line.
• When writing and using local headers:
• Try to avoid cyclic header inclusion dependencies.
• Instead ensure they are included where and when they are needed.
• Read Go import design
• Read Plan 9 compiler notes

User Defined Types

• Do not use type_t naming (it is reserved for POSIX and less readable).
• Typedef opaque structs.
• Do not typedef builtin types.
• Use CamelCase for typedef'd types.

Line Length

• Keep lines to reasonable length (max 79 characters).

Tests and Boolean Values

• Do not use C99 bool types (stick to integer types).

• Otherwise use compound assignment and tests unless the line grows too long: