xref: /src/share/misc/style

/*
 * Style guide for the 4BSD KNF (Kernel Normal Form).
 *
 *	from: @(#)style	1.12 (Berkeley) 3/18/94
 *	$Id: style,v 1.2 1994/03/26 03:24:54 cgd Exp $
 */

/*
 * VERY important single-line comments look like this.
 */

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

/*
 * Multi-line comments look like this.  Make them real sentences.  Fill
 * them so they look like real paragraphs.
 */

/*
 * Kernel include files come first; normally, you'll need <sys/types.h>
 * OR <sys/param.h>, but not both!  <sys/types.h> includes <sys/cdefs.h>,
 * and it's okay to depend on that.
 */
#include <sys/types.h>		/* Non-local includes in brackets. */

/* If it's a network program, put the network include files next. */
#include <net/if.h>
#include <net/if_dl.h>
#include <net/route.h>
#include <netinet/in.h>
#include <protocols/rwhod.h>

/*
 * Then there's a blank line, followed by the /usr include files.
 * The /usr include files should be sorted!
 */
#include <stdio.h>

/*
 * Global pathnames are defined in /usr/include/paths.h.  Pathnames local
 * to the program go in pathnames.h in the local directory.
 */
#include <paths.h>

/* Then, there's a blank line, and the user include files. */
#include "pathnames.h"		/* Local includes in double quotes. */		

/*
 * ANSI function declarations for private functions (i.e. functions not used
 * elsewhere) go at the top of the source module.  Use the __P macro from
 * the include file <sys/cdefs.h>.  Only the kernel has a name associated with
 * the types, i.e. in the kernel use:
 *
 *	void function __P((int a));
 *
 * in user land use:
 *
 *	void function __P((int));
 */
static char	*function __P((int, const char *));
static void	 usage __P((void));

/*
 * Macros are capitalized, parenthesized, and should avoid side-effects.
 * If they are an inline expansion of a function, the function is defined
 * all in lowercase, the macro has the same name all in uppercase. If the
 * macro needs more than a single line, use braces.  Right-justify the
 * backslashes, it makes it easier to read.
 */
#define	MACRO(x, y) {							\
	variable = (x) + (y);						\
	(y) += 2;							\
}

/* Enum types are capitalized. */
enum enumtype { ONE, TWO } et;

/*
 * When declaring variables in structures, declare them sorted by use, then
 * by size, and then by alphabetical order.  The first category normally
 * doesn't apply, but there are exceptions.  Each one gets its own line.
 * Put a tab after the first word, i.e. use "int^Ix;" and "struct^Ifoo *x;".
 *
 * 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.
 */
struct foo {
	struct	foo *next;	/* List of active foo */
	struct	mumble amumble;	/* Comment for mumble */
	int	bar;
};
struct foo *foohead;		/* Head of global foo list */

/* Make the structure name match the typedef. */
typedef struct _bar {
	int	level;
} BAR;
	
/*
 * 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(argc, argv)
	int argc;
	char *argv[];
{
	extern char *optarg;
	extern int optind;
	long num;
	int ch;
	char *ep;

	/*
	 * For consistency, getopt should be used to parse options.  Options
	 * should be sorted in the getopt 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.
	 */
	while ((ch = getopt(argc, argv, "abn")) != EOF)
		switch (ch) {		/* Indent the switch. */
		case 'a':		/* Don't indent the case. */
			aflag = 1;
			/* FALLTHROUGH */
		case 'b':
			bflag = 1;
			break;
		case 'n':
			num = strtol(optarg, &ep, 10);
                        if (num <= 0 || *ep != '\0')
                                err("illegal number -- %s", optarg);
			break;
		case '?':
		default:
			usage();
			/* NOTREACHED */
		}
	argc -= optind;
	argv += optind;

	/*
	 * Space after keywords (while, for, return, switch).  No braces are
	 * used for control statements with zero or only a single statement.
	 *
	 * Forever loops are done with for's, not while's.
	 */
	for (p = buf; *p != '\0'; ++p);
	for (;;)
		stmt;
	
	/*
	 * Parts of a for loop may be left empty.  Don't put declarations
	 * inside blocks unless the routine is unusually complicated.
	 */
	for (; cnt < 15; cnt++) {
		stmt1;
		stmt2;
	}

	/* Second level indents are four spaces. */
	while (cnt < 20)
		z = a + really + long + statment + that + needs + two lines +
		    gets + indented + four + spaces + on + the + second +
		    and + subsequent + lines.

	/*
	 * Closing and opening braces go on the same line as the else.
	 * Don't add braces that aren't necessary.
	 */
	if (test)
		stmt;
	else if (bar) {
		stmt;
		stmt;
	} else
		stmt;
		
	/* No spaces after function names. */
	if (error = function(a1, a2))
		exit(error);

	/*
	 * Unary operators don't require spaces, binary operators do. Don't
	 * use parenthesis unless they're required for precedence, or the
	 * statement is really confusing without them.
	 */
	a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
	k = !(l & FLAGS);

	/*
	 * Exits should be 0 on success, and 1 on failure.  Don't denote
	 * all the possible exit points, using the integers 1 through 300.
	 */
	exit(0);    /* Avoid obvious comments such as "Exit 0 on success." */
}

/*
 * If a function type is declared, it should be on a line
 * by itself preceeding the function.
 */
static char *
function(a1, a2, fl, a4)
	int a1, a2, a4;	/* Declare ints, too, don't default them. */
	float fl;	/* List in order declared, as much as possible. */
{
	/*
	 * When declaring variables in functions declare them sorted by size,
	 * then in alphabetical order; multiple ones per line are okay.  Old
	 * style function declarations can go on the same line.  ANSI style
	 * function declarations should go in the include file "externs.h".
	 * If a line overflows reuse the type keyword.
	 *
	 * DO NOT initialize variables in the declarations.
	 */
	extern u_char one;
	extern char two;
	struct foo three, *four;
	double five;
	int *six, seven, eight();
	char *nine, ten, eleven, twelve, thirteen, fourteen, fifteen, sixteen;
	char *overflow __P((void));
	void *mymalloc __P((u_int));

	/*
	 * Casts and sizeof's are not followed by a space.  NULL is any
	 * pointer type, and doesn't need to be cast, so use NULL instead
	 * of (struct foo *)0 or (struct foo *)NULL.  Also, test pointers
	 * against NULL, i.e. use:
	 *
	 * 	(p = f()) == NULL
	 * not:
	 *	!(p = f())
	 *
	 * Don't use '!' for tests unless it's a boolean, e.g. use
	 * "if (*p == '\0')", not "if (!*p)".
 	 *
	 * Routines returning void * should not have their return values cast
	 * to any pointer type.
	 *
	 * Use err/warn(3), don't roll your own!
	 */
	if ((four = malloc(sizeof(struct foo))) == NULL)
		err(1, NULL);
	if ((six = (int *)overflow()) == NULL)
		errx(1, "Number overflowed.");
	return (eight);
}

/*
 * Don't use ANSI function declarations unless you absolutely have too,
 * i.e. you're declaring functions with variable numbers of arguments.
 *
 * ANSI function braces look like regular function braces.
 */
function(int a1, int a2)
{
	...
}

/* Variable numbers of arguments should look like this. */
#if __STDC__
#include <stdarg.h>
#else
#include <varargs.h>
#endif

void
#if __STDC__
vaf(const char *fmt, ...)
#else
vaf(fmt, va_alist)
	char *fmt;
	va_dcl
#endif
{
	va_list ap;
#if __STDC__
	va_start(ap, fmt);
#else
	va_start(ap);
#endif
	STUFF;

	va_end(ap);		/* No return needed for void functions. */
}

static void
usage()
{	/* Insert an empty line if the function has no local variables. */

	/*
	 * Use printf(3), not fputs/puts/putchar/whatever, it's faster and
	 * usually cleaner, not to mention avoiding stupid bugs.
	 *
	 * Usage statements should look like the manual pages.  Options w/o
	 * operands come first, in alphabetical order inside a single set of
	 * braces.  Followed by options with operands, in alphabetical order,
	 * each in braces.  Followed by required arguments in the order they
	 * are specified, followed by optional arguments in the order they
	 * are specified.  A bar ('|') separates either/or options/arguments,
	 * and multiple options/arguments which are specified together are
	 * placed in a single set of braces.
	 *
	 * "usage: f [-ade] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\n"
	 * "usage: f [-a | -b] [-c [-de] [-n number]]\n"
	 */
	(void)fprintf(stderr, "usage: f [-ab]\n");
	exit(1);
}