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$Id$
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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 <paths.h>. 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&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 <bsd.prog.mk> and there is a single
source file named the same as the PROG.</para>
<para>Omit MAN when using <bsd.prog.mk> 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 <bsd.*.mk> goes last.</para>
<para>Do not use anachronisms like $< 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>