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<article>

  <articleinfo>

    <title>Style Guide</title>

    <corpauthor>The TenDRA Project</corpauthor>

    <author>

      <firstname>Jeroen</firstname>

      <surname>Ruigrok van der Werven</surname>

    </author>

    <authorinitials>JRvdW</authorinitials>

    <pubdate>2005</pubdate>

    <copyright>

      <year>2005</year>

      <holder>The TenDRA Project</holder>

    </copyright>

  </articleinfo>

  <sect1 id="introduction">

    <title>Introduction</title>

  </sect1>

  <sect1 id="coding-style">

    <title>Coding Style</title>

    <programlisting>

/* Most single-line comments look like this. */

    </programlisting>

    <programlisting>

/*

 * VERY important single-line comments look like this.

 */

    </programlisting>

    <programlisting>

/*

 * Multi-line comments look like this.  Make them real sentences.  Fill

 * them so they look like real paragraphs.

 */

    </programlisting>

    <para>The copyright header should be a multi-line comment:</para>

    <programlisting>

/*

 * Copyright (c) 1984-2025 John Q. Public.  All Rights Reserved.

 *

 * Long, boring license goes here, but redacted for brevity

 */

    </programlisting>

    <para>After any copyright header, there is a blank line, and the rcsid for

      source files.  Version control system ID tags should only exist once in

      a file (unlike in this one).  Non-C/C++ source files follow the example

      above, while C/C++ source files follow the one below.  All VCS (version

      control system) revision identification in files obtained from elsewhere

      should be maintained, including, where applicable, multiple IDs showing

      a file's history.  In general, do not edit foreign IDs or their

      infrastructure.  Unless otherwise wrapped (such as #if

      defined(LIBC_SCCS)), enclose both in #if 0 ...  #endif to hide any

      uncompilable bits and to keep the IDs out of object files.  Only add

      From: in front of foreign VCS IDs if the file is renamed.</para>

    <programlisting>

#if 0

#ifndef lint

static char sccsid[] = "@(#)style       1.14 (Berkeley) 4/28/95";

#endif /* not lint */

#endif

#include <sys/cdefs.h>

__FBSDID("$FreeBSD: src/share/man/man9/style.9,v 1.110.2.1 2005/03/01 12:44:49 brueffer Exp $");

    </programlisting>

    <para>Leave another blank line before the header files.</para>

    <para>Kernel include files (i.e. sys/*.h) come first; normally, include

      <sys/types.h> OR <sys/param.h> but not both.

      <sys/types.h> includes <sys/cdefs.h> and it is okay to

      depend on that.</para>

    <programlisting>

#include <sys/types.h>  /* Non-local includes in angle brackets. */

    </programlisting>

    <para>Leave a blank line before the next group, the /usr/include files,

      which should be sorted alphabetically by name.</para>

     <programlisting>

#include <stdio.h>

     </programlisting>

    <para>Global pathnames are defined in &lt;paths.h&gt;.  Pathnames local to

      the program go in "pathnames.h" in the local directory.</para>

    <programlisting>

#include <paths.h>

    </programlisting>

    <para>Leave another blank line before the user include files.</para>

     #include "pathnames.h"          /* Local includes in double quotes. */

    <para>Do not #define or declare names in the implementation namespace

      except for implementing application interfaces.</para>

    <para>The names of unsafe macros (ones that have side effects), and the

      names of macros for manifest constants, are all in uppercase.  The

      expansions of expression-like macros are either a single token or have

      outer parentheses.  Put a single tab character between the #define and

      the macro name.  If a macro is an inline expansion of a function, the

      function name is all in lowercase and the macro has the same name all in

      uppercase.  Right-justify the backslashes; it makes it easier to read.

      If the macro encapsulates a compound statement, enclose it in a do loop,

      so that it can safely be used in if statements.  Any final

      statement-terminating semicolon should be supplied by the macro

      invocation rather than the macro, to make parsing easier for

      pretty-printers and editors.</para>

    <programlisting>

#define MACRO(x, y) do {                                                \

        variable = (x) + (y);                                           \

        (y) += 2;                                                       \

} while (0)

   </programlisting>

    <para>When code is conditionally compiled using #ifdef or #if, a comment

      may be added following the matching #endif or #else to permit the reader

      to easily discern where conditionally compiled code regions end.  This

      comment should be used only for (subjectively) long regions, regions

      greater than 20 lines, or where a series of nested #ifdefs may be

      confusing to the reader.  Exceptions may be made for cases where code is

      conditionally not compiled for the purposes of lint(1), even though the

      uncompiled region may be small.  The comment should be separated from

      the #endif or #else by a single space.  For short conditionally compiled

      regions, a closing comment should not be used.</para>

    <para>The comment for #endif should match the expression used in the

      corresponding #if or #ifdef.  The comment for #else and #elif should

      match the inverse of the expression(s) used in the preceding #if and/or

      #elif statements.  In the comments, the subexpression defined(FOO) is

      abbreviated as FOO.  For the purposes of comments, #ifndef FOO is

      treated as #if !defined(FOO).</para>

    <programlisting>

#ifdef KTRACE

#include <sys/ktrace.h>

#endif

#ifdef COMPAT_43

/* A large region here, or other conditional code. */

#else /* !COMPAT_43 */

/* Or here. */

#endif /* COMPAT_43 */

#ifndef COMPAT_43

/* Yet another large region here, or other conditional code. */

#else /* COMPAT_43 */

/* Or here. */

#endif /* !COMPAT_43 */

    </programlisting>

    <para>The project is slowly moving to use the ISO/IEC 9899:1999 (ISO

      C99) unsigned integer identifiers of the form uintXX_t in preference to

      the older BSD style integer identifiers of the form u_intXX_t.  New code

      should use the former, and old code should be converted to the new form

      if other major work is being done in that area and there is no

      overriding reason to prefer the older BSD style.  Like white space

      commits, care should be taken in making uintXX_t only commits.</para>

    <para>Enumeration values are all uppercase.</para>

    <programlisting>

enum enumtype { ONE, TWO } et;

    </programlisting>

    <para>In declarations, do not put any whitespace between asterisks and

      adjacent tokens, except for tokens that are identifiers related to

      types.  (These identifiers are the names of basic types, type

      qualifiers, and typedef names other than the one being declared.)

      Separate these identifiers from asterisks using a single space.</para>

    <para>When declaring variables in structures, declare them sorted by use,

      then by size (largest to smallest), and then in alphabetical order.  The

      first category normally does not apply, but there are exceptions.  Each

      one gets its own line.  Try to make the structure readable by aligning

      the member names using either one or two tabs depending upon your

      judgment.  You should use one tab only if it suffices to align at least

      90% of the member names.  Names following extremely long types should be

      separated by a single space.</para>

    <para>Major structures should be declared at the top of the file in which

      they are used, or in separate header files if they are used in multiple

      source files.  Use of the structures should be by separate declarations

      and should be extern if they are declared in a header file.</para>

    <programlisting>

struct foo {

        struct foo      *next;          /* List of active foo. */

        struct mumble   amumble;        /* Comment for mumble. */

        int             bar;            /* Try to align the comments. */

        struct verylongtypename *baz;   /* Won't fit in 2 tabs. */

};

struct foo *foohead;                    /* Head of global foo list. */

    </programlisting>

    <para>Use queue(3) macros rather than rolling your own lists, whenever

      possible.  Thus, the previous example would be better written:</para>

    <programlisting>

#include <sys/queue.h>

struct foo {

        LIST_ENTRY(foo) link;           /* Use queue macros for foo lists. */

        struct mumble   amumble;        /* Comment for mumble. */

        int             bar;            /* Try to align the comments. */

        struct verylongtypename *baz;   /* Won't fit in 2 tabs. */

};

LIST_HEAD(, foo) foohead;               /* Head of global foo list. */

    </programlisting>

    <para>Avoid using typedefs for structure types.  Typedefs are problematic

      because they do not properly hide their underlying type; for example you

      need to know if the typedef is the structure itself or a pointer to the

      structure.  In addition they must be declared exactly once, whereas an

      incomplete structure type can be mentioned as many times as necessary.

      Typedefs are difficult to use in stand-alone header files: the header

      that defines the typedef must be included before the header that uses

      it, or by the header that uses it (which causes namespace pollution), or

      there must be a back-door mechanism for obtaining the typedef.</para>

    <para>When convention requires a typedef, make its name match the struct

      tag.  Avoid typedefs ending in _t, except as specified in Standard C

      or by POSIX.</para>

    <programlisting>

/* Make the structure name match the typedef. */

typedef struct bar {

        int     level;

} BAR;

typedef int             foo;            /* This is foo. */

typedef const long      baz;            /* This is baz. */

   </programlisting>

   <para>All functions are prototyped somewhere.</para>

   <para>Function prototypes for private functions (i.e., functions not used

     elsewhere) go at the top of the first source module.  Functions local

     to one source module should be declared static.</para>

    <para>Function prototypes should be listed in a logical order, preferably

      alphabetical unless there is a compelling reason to use a different

      ordering.</para>

    <para>Functions that are used locally in more than one module go into a

      separate header file, e.g. "extern.h".</para>

    <para>Do not use the __P macro.</para>

    <para>In general code can be considered new code when it makes up about

      50% or more of the file(s) involved.  This is enough to break precedents

      in the existing code and use the current style guidelines.</para>

    <para>In header files visible to userland applications, prototypes that

      are visible must use either protected names (ones beginning with an

      underscore) or no names with the types.  It is preferable to use

      protected names.  E.g., use:</para>

    <programlisting>

void    function(int);

    </programlisting>

    <para>or:</para>

    <programlisting>

void    function(int _fd);

    </programlisting>

    <para>Prototypes may have an extra space after a tab to enable function

      names to line up:</para>

    <programlisting>

static char     *function(int _arg, const char *_arg2, struct foo *_arg3,

                          struct bar *_arg4);

static void      usage(void);

/*

 * All major routines should have a comment briefly describing what

 * they do.  The comment before the "main" routine should describe

 * what the program does.

 */

int

main(int argc, char *argv[])

{

        char *ep;

        long num;

        int ch;

    </programlisting>

    <para>For consistency, getopt(3) should be used to parse options.  Options

      should be sorted in the getopt(3) call and the switch statement, unless

      parts of the switch cascade.  Elements in a switch statement that

      cascade should have a FALLTHROUGH comment.  Numerical arguments should

      be checked for accuracy.  Code that cannot be reached should have a

      NOTREACHED comment.</para>

    <programlisting>

while ((ch = getopt(argc, argv, "abNn:")) != 1)

        switch (ch) {           /* Indent the switch. */

        case a:               /* Don't indent the case. */

                aflag = 1;

                /* FALLTHROUGH */

        case b:

                bflag = 1;

                break;

        case N:

                Nflag = 1;

                break;

        case n:

                num = strtol(optarg, &ep, 10);

                if (num <= 0 || *ep != '\0') {

                        warnx("illegal number, -n argument -- %s",

                            optarg);

                        usage();

                }

                break;

        case '?':

        default:

                usage();

                /* NOTREACHED */

        }

argc -= optind;

argv += optind;

    </programlisting>

    <para>Space after keywords (if, while, for, return, switch).  No braces

      ({ and }) are used for control statements with zero or only a single

      statement unless that statement is more than a single line in which case

      they are permitted.  Forever loops are done with for's, not

      while's.</para>

    <programlisting>

for (p = buf; *p != '\0'; ++p)

        ;       /* nothing */

for (;;)

        stmt;

for (;;) {

        z = a + really + long + statement + that + needs +

            two + lines + gets + indented + four + spaces +

            on + the + second + and + subsequent + lines;

}

for (;;) {

        if (cond)

                stmt;

}

if (val != NULL)

        val = realloc(val, newsize);

    </programlisting>

    <para>Parts of a for loop may be left empty.  Do not put declarations

      inside blocks unless the routine is unusually complicated.</para>

    <programlisting>

for (; cnt < 15; cnt++) {

        stmt1;

        stmt2;

}

    </programlisting>

    <para>Indentation is an 8 character tab.  Second level indents are four

      spaces.  If you have to wrap a long statement, put the operator at the

      end of the line.</para>

    <programlisting>

while (cnt < 20 && this_variable_name_is_too_long &&

    ep != NULL)

        z = a + really + long + statement + that + needs +

            two + lines + gets + indented + four + spaces +

            on + the + second + and + subsequent + lines;

    </programlisting>

    <para>Do not add whitespace at the end of a line, and only use tabs

      followed by spaces to form the indentation.  Do not use more spaces than

      a tab will produce and do not use spaces in front of tabs.</para>

     <para>Closing and opening braces go on the same line as the else.  Braces

       that are not necessary may be left out.</para>

    <programlisting>

if (test)

        stmt;

else if (bar) {

        stmt;

        stmt;

} else

        stmt;

    </programlisting>

    <para>No spaces after function names.  Commas have a space after them.  No

      spaces after ( or [ or preceding ] or ) characters.</para>

    <programlisting>

error = function(a1, a2);

if (error != 0)

        exit(error);

    </programlisting>

    <para>Unary operators do not require spaces, binary operators do.  Do not

      use parentheses unless they are required for precedence or unless the

      statement is confusing without them.  Remember that other people may

      confuse easier than you.  Do YOU understand the following?</para>

    <programlisting>

a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;

k = !(l & FLAGS);

    </programlisting>

    <para>Exits should be 0 on success, or according to the predefined values

      in sysexits(3).</para>

    <programlisting>

        exit(EX_OK);    /*

                         * Avoid obvious comments such as

                         * "Exit 0 on success."

                         */

}

    </programlisting>

    <para>The function type should be on a line by itself preceding the

      function.  The opening brace of the function body should be on a line by

      itself.</para>

    <programlisting>

static char *

function(int a1, int a2, float fl, int a4)

{

    </programlisting>

    <para>When declaring variables in functions declare them sorted by size,

      then in alphabetical order; multiple ones per line are okay.  If a line

      overflows reuse the type keyword.</para>

     <para>Be careful to not obfuscate the code by initializing variables in

       the declarations.  Use this feature only thoughtfully.  DO NOT use

       function calls in initializers.</para>

    <programlisting>

struct foo one, *two;

double three;

int *four, five;

char *six, seven, eight, nine, ten, eleven, twelve;

four = myfunction();

    </programlisting>

    <para>Do not declare functions inside other functions; ANSI C says that

      such declarations have file scope regardless of the nesting of the

      declaration.  Hiding file declarations in what appears to be a local

      scope is undesirable and will elicit complaints from a good

      compiler.</para>

    <para>Casts and sizeof's are not followed by a space.  Note that indent(1)

      does not understand this rule.  sizeof's are written with parenthesis

      always.  The redundant parenthesis rules do not apply to sizeof(var)

      instances.</para>

     <para>NULL is the preferred null pointer constant.  Use NULL instead of

       (type *)0 or (type *)NULL in contexts where the compiler knows the

       type, e.g., in assignments.  Use (type *)NULL in other contexts, in

       particular for all function args.  (Casting is essential for variadic

       args and is necessary for other args if the function prototype might

       not be in scope.) Test pointers against NULL, e.g., use:</para>

    <programlisting>

(p = f()) == NULL

    </programlisting>

    <para>not:</para>

    <programlisting>

!(p = f())

    </programlisting>

    <para>Do not use !! for tests unless it is a boolean, e.g. use:</para>

    <programlisting>

if (*p == '\0')

    </programlisting>

    <para>not:</para>

    <programlisting>

if (!*p)

    </programlisting>

    <para>Routines returning void * should not have their return values cast

      to any pointer type.</para>

    <para>Values in rreettuurrnn statements should be enclosed in

      parentheses.</para>

    <para>Use err(3) or warn(3), do not roll your own.</para>

    <programlisting>

        if ((four = malloc(sizeof(struct foo))) == NULL)

                err(1, (char *)NULL);

        if ((six = (int *)overflow()) == NULL)

                errx(1, "number overflowed");

        return (eight);

}

    </programlisting>

    <para>Old-style function declarations look like this:</para>

    <programlisting>

static char *

function(a1, a2, fl, a4)

        int a1, a2;     /* Declare ints, too, don't default them. */

        float fl;       /* Beware double vs. float prototype differences. */

        int a4;         /* List in order declared. */

{

    </programlisting>

    <para>Use ANSI function declarations unless you explicitly need K&amp;R

      compatibility.  Long parameter lists are wrapped with a normal four

      space indent.</para>

    <para>Variable numbers of arguments should look like this:</para>

    <programlisting>

#include <stdarg.h>

void

vaf(const char *fmt, ...)

{

        va_list ap;

        va_start(ap, fmt);

        STUFF;

        va_end(ap);

        /* No return needed for void functions. */

}

static void

usage()

{

        /* Insert an empty line if the function has no local variables. */

    </programlisting>

    <para>Use printf(3), not fputs(3), puts(3), putchar(3), whatever; it is

      faster and usually cleaner, not to mention avoiding stupid bugs.</para>

    <para>Usage statements should look like the manual pages SYNOPSIS.  The

      usage statement should be structured in the following order:</para>

    <itemizedlist>

      <listitem>Options without operands come first, in alphabetical order,

        inside a single set of brackets ([ and ]).</listitem>

      <listitem>Options with operands come next, also in alphabetical order,

        with each option and its argument inside its own pair of

        brackets.</listitem>

      <listitem>Required arguments (if any) are next, listed in the order they

        should be specified on the command line.</listitem>

      <listitem>Finally, any optional arguments should be listed, listed in

        the order they should be specified, and all inside

        brackets.</listitem>

    </itemizedlist>

    <para>A bar (|) separates either - or options/arguments, and multiple

      options/arguments which are specified together are placed in a single

      set of brackets.</para>

    <programlisting>

    "usage: f [-aDde] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\n"

    "usage: f [-a | -b] [-c [-dEe] [-n number]]\n"

        (void)fprintf(stderr, "usage: f [-ab]\n");

        exit(EX_USAGE);

}

    </programlisting>

    <para>Note that the manual page options description should list the

      options in pure alphabetical order.  That is, without regard to whether

      an option takes arguments or not.  The alphabetical ordering should take

      into account the case ordering shown above.</para>

    <para>Stylistic changes (including whitespace changes) are hard on the

      source repository and are to be avoided without good reason.  Code that

      is approximately FreeBSD KNF style compliant in the repository must not

      diverge from compliance.</para>

    <para>Whenever possible, code should be run through a code checker (e.g.,

      lint(1) or gcc Wall) and produce minimal warnings.</para>

    <para>All makefiles should have an SCM ID at the start of the file,

      followed by a blank line.</para>

    <programlisting>

# $FreeBSD$

    </programlisting>

    <para>.PATH: comes next if needed, and is spelled .PATH: , with a single

      ASCII space after a colon.  Do not use the VPATH variable.</para>

    <para>Special variables (i.e., LIB, SRCS, MLINKS, etc.) are listed in

      order of product, then building and installing a binary.  Special

      variables may also be listed in build order: i.e., ones for the primary

      program (or library) first.  The general product order is:

      PROG/[SH]LIB/SCRIPTS FILES LINKS [NO]MAN MLINKS INCS SRCS WARNS CFLAGS

      DPADD LDADD.  The general build order is: PROG/[SH]LIB/SCRIPTS SRCS

      WARNS CFLAGS DPADD LDADD INCS FILES LINKS [NO]MAN MLINKS.</para>

    <para>Omit SRCS when using &lt;bsd.prog.mk&gt; and there is a single

      source file named the same as the PROG.</para>

    <para>Omit MAN when using &lt;bsd.prog.mk&gt; and the manual page is

      named the same as the PROG, and is in section 1.</para>

    <para>All variable assignments are spelled VAR==, i.e., no space between

      the variable name and the ==.  Keep values sorted alphabetically, if

      possible.</para>

    <para>Do not use ++== to set variables that are only set once (or to set

      variables for the first time).</para>

    <para>Do not use vertical whitespace in simple makefiles, but do use it to

      group locally related things in more complex/longer ones.</para>

    <para>WARNS comes before CFLAGS, as it is basically a CFLAGS modifier.  It

      comes before CFLAGS rather than after CFLAGS so it does not get lost in

      a sea of CFLAGS statements as WARNS is an important thing.  The usage of

      WARNS is spelled WARNS?= , so that it may be overridden on the command

      line or in /etc/make.conf.</para>

    <para>NO_WERROR= yes should not be used, it defeats the purpose of WARNS.

      It should only be used on the command line and in special circum

      stances.</para>

    <para>CFLAGS is spelled CFLAGS+= .</para>

    <para>Listing D's before I's in CFLAGS is preferred for alphabetical

      ordering and to make D's easier to see.  The D's often affect

      conditional compilation, and I's tend to be quite long.  Split long

      CFLAGS settings between the D's and I's.</para>

    <para>Do not use GCCisms (such as g and Wall) in CFLAGS.</para>

    <para>Typically, there is one ASCII tab between VAR== and the value in

      order to start the value in column 9.  An ASCII space is allowed for

      variable names that extend beyond column 9.  A lack of whitespace is

      also allowed for very long variable names.</para>

    <para>.include &lt;bsd.*.mk&gt; goes last.</para>

    <para>Do not use anachronisms like $&lt; and $@.  Instead use ${.IMPSRC}

      or ${.ALLSRC} and ${.TARGET}.</para>

    <para>The desire to express a logical grouping often means not obeying

      some of the above.</para>

    <para>The simplest program Makefile is:</para>

    <programlisting>

# $FreeBSD$

PROG=   foo

.include <bsd.prog.mk>

    </programlisting>

    <para>The simplest library Makefile is:</para>

    <programlisting>

# $FreeBSD$

LIB=    foo

SHLIB_MAJOR= 1

MAN=    libfoo.3

SRCS=   foo.c

.include <bsd.lib.mk>

    </programlisting>

  </sect1>

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    href="../common/colophon.xml"/>

</article>