Coding style for C programs

This document describes the coding style I try to enforce in C source code. This is, mostly, “K&R style” but with a few variations.

Indentation

• Indentation level is 4 spaces.
• Use either spaces only, or a mix of tabs and spaces (not quite decided yet). If using tabs and spaces, always use 8-stop tabs (that is, never change the editor’s setting of what a tab is).

Function definitions and prototypes

• The return type of a function is on its own line before the function name and the list of arguments, both in the prototype and in the definition.
• No spaces between the function name and the opening paren.
• No spaces between the parens and the arguments inside.
• The braces enclosing the function body are on their own line, on the first column.
• Arguments in prototypes are named.
• Arguments are all on the same line when possible (if the function name and the arguments list fit on a 78-characters line). Otherwise:
  • each argument is on its own line;
  • the first argument is on the same line than the function name;
  • the last argument is on the same line than the closing paren;
  • arguments are aligned on the column next to the opening paren;
  • argument names are aligned on the closest common column after the types, leaving one intervening space;
  • pointer marks are “dangling” on the left of argument names.
• When calling a function, if the argument list does not fit in a single line, dispatch arguments only on as many lines as necessary (do not put each argument on its own line).

Example:

static int
foo_bar(int         frobnicate,
        const char *src,
        const char *dst,
        double      foo_ratio,
        int         bar_type)
{
    function_with_an_absurdly_long_name(frobnicate, (char *)src, dst,
                                        foo_ratio, bar_type);
}

Control flow

• No braces around single-statement conditional blocks.
• The opening brace of a conditional block is on the same line than the associated if, for, while, do, or else keyword, and is preceded by a space.
• The closing brace of a conditional block is on its own line, aligned with the associated control keyword.
• A else keyword is on the line following the associated if-block.
• In a do-while loop, the while keyword is on the same line than the closing brace of the do-block.
• There is one space between all control flow keywords and the following opening paren.
• There is a space before and after the conditional expression inside the parens. But there is no spaces inside nested parens.
• There is one space after the ! operator.

Examples:

if ( foo ) {
    /* ... */
}
else if ( ! bar ) {
    /* ... */
}

do {
    /* ... */
} while ( foo && ! (bar < 0 && frob != 2) );

Using GNU Indent

The following options for GNU Indent can be used to approximate the style described above (except the spaces around the conditional expression inside the parens—the -prs option makes no distinction between the outermost parens and the nested parens):

-kr -blf -nce -l78 -psk -sc -nut -ss

Naming convention

• Function, variable, and type names are in lowercase with words separated by underscores.
• Preprocessor symbols and enum values are in uppercase, again with underscores.
• Aliased types are suffixed with _t.