Indent Style | CΛTΞИCOΔΞ

/in-ˈdent stī(-ə)l/

[C programmers]

n. The rules one uses to indent code in a readable fashion; a subject of holy wars. There are four major C indent styles, described below; all have the aim of making it easier for the reader to visually track the scope of control constructs. The significant variable is the placement of { and } with respect to the statement(s) they enclose and the guard or controlling statement (if, else, for, while, or do) on the block, if any.

K&R style

Named after Kernighan & Ritchie, because the examples in K&R are formatted this way. Also called kernel style because the UNIX kernel is written in it, and the One True Brace Style (abbrev. 1TBS) by its partisans. The basic indent shown here is eight spaces (or one tab) per level; four or are occasionally seen, but are much less common.

int max(int a, int b) {
    if (a > b) {
        return a;
    } else {
        return b;
    }
}

Allman style

Named for Eric Allman, a Berkeley hacker who wrote a lot of the BSD utilities in it (it is sometimes called BSD style). Resembles normal indent style in Pascal and Algol. Basic indent per level shown here is eight spaces, but four is just as common (esp. in C++ code).

int max(int a, int b)
{
    if (a > b)
    {
        return a;
    }
    else
    {
        return b;
    }
}

Whitesmiths style

Popularized by the examples that came with Whitesmiths C, an early commercial C compiler. Basic indent per level shown here is eight spaces, but four is occasionally seen.

int max(int a, int b)
    {
    if (a > b)
        {
        return a;
        }
    else
        {
        return b;
        }
    }

Used throughout GNU EMACS and the Free Software Foundation code, and just about nowhere else. Indents are always four spaces per level, with { and } halfway between the outer and inner indent levels.

int max (int a, int b)
{
  if (a > b)
    {
      return a;
    }
  else
    {
      return b;
    }

Surveys have shown the Allman and Whitesmiths styles to be the most common, with about equal mind shares. K&R/1TBS used to be nearly universal, but is now much less common (the opening brace tends to get lost against the right parenthesis of the guard part in an if or while, which is a Bad Thing). Defenders of 1TBS argue that any putative gain in readability is less important than their style's relative economy with vertical space, which enables one to see more code on one's screen at once. Doubtless these issues will continue to be the subject of holy wars.

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