C Style Guide

This document gives general guidelines on generic C style and code formatting within Sofia-SIP.

The guidelines include identifier naming conventions, indenting convention, and tool usage directions.

Please note that C style is always a matter of taste.

Naming Conventions

Generally, identifiers within each module are prefixed with the name of that module. For instance, the functions within http parser module http have prefix http_. Identifiers composed of multiple words have an underscore "_" between the words, the words themselves are in lower case. For instance, http_request_create().

Macros should be in upper case. File names should be in lower case using underscore as delimiter if needed.

Normal typedefs have suffix _t, however, function types have suffix _f. The enum names also sometimes have _e, struct names have _s and union names _u.

It is recommended that type itself is typedef'ed, not a pointer to the type. It should be clear from variable declaration if the variable is a pointer or not.

typedef struct foo_s foo_t;
typedef int f_fun(foo_t *f, char const *s);

Struct and union members should have common prefix. For instance,

struct foo_s {
  int    f_len;
  char  *f_name;
  fun_f *f_fun;
};

This prefix makes it easier to find where members are used.

Indenting and Formatting code

Indentation in Sofia-SIP C code generally follows the K&R style with indent of 2 characters (so you can use the default "GNU" c-style in Emacs). The maximum line length should be 80 characters.

For example,

void kluge(int foo)
{
  if (foo) {
    bar();
  }
  else {
    switch (baz()) {
    case a:
      eeny();
      break;
    case b:
      meeny();
      break;
    default:
      moe();
      break;
    }
  }
}

The default indentation can be achieved with GNU indent with options

-nbad -bap -bbo -nbc -br -brs -c33 -cd33 -ncdb -ce -ci2 -cli0 -cp33 -cs
-d0 -di1 -nfc1 -nfca -hnl -i2 -ip0 -l79 -lp -npcs -nprs -npsl -saf -sai
-saw -nsc -nsob -nss

Loops without condition use for (;;) instead of while (1).

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

There should be whitespace on both sides of infix operators, except . or ->, which require no space, or , (comma) which requires space only after). There should be whitespace between a keyword and parenthesis following it, but no whitespace between an identifier and parenthesis following it. E.g.,

  while (i++ < n)
    baz();
  for (;;) {
    x->x_foo();
    if (bar())
      break;
    z.z_baz++;
  }
  return (13 * i);