516 lines
15 KiB
Groff
516 lines
15 KiB
Groff
.\" Copyright (c) 1995 FreeBSD Inc.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL [your name] OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd December 14, 1995
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.Dt STYLE 9
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.Os FreeBSD
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.Sh NAME
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.Nm style
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.Nd "Kernel source file style guide"
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.Sh DESCRIPTION
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This file specifies the preferred style for kernel source files in the
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.Tn FreeBSD
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source tree. It is also a guide for preferred userland code style.
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.Bd -literal -offset 0i
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/*
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* Style guide for the FreeBSD KNF (Kernel Normal Form).
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*/
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/*
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* VERY important single-line comments look like this.
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*/
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/* Most single-line comments look like this. */
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/*
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* Multi-line comments look like this. Make them real sentences. Fill
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* them so they look like real paragraphs.
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*/
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.Ed
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.Pp
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Kernel include files (i.e. sys/*.h) come first; normally, you'll need
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<sys/types.h>
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OR <sys/param.h>, but not both! <sys/types.h> includes <sys/cdefs.h>,
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and it's okay to depend on that.
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.Bd -literal -offset 0i
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#include <sys/types.h> /* Non-local includes in brackets. */
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.Ed
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.Pp
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If it's a network program, put the network include files next.
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.Bd -literal -offset 0i
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#include <net/if.h>
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#include <net/if_dl.h>
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#include <net/route.h>
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#include <netinet/in.h>
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#include <protocols/rwhod.h>
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.Ed
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.Pp
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Then there's a blank line, followed by the /usr include files.
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The /usr include files should be sorted!
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.Bd -literal -offset 0i
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#include <stdio.h>
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.Ed
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.Pp
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Global pathnames are defined in /usr/include/paths.h. Pathnames local
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to the program go in pathnames.h in the local directory.
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.Bd -literal -offset 0i
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#include <paths.h>
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.Ed
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.Pp
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Then, there's a blank line, and the user include files.
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.Bd -literal -offset 0i
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#include "pathnames.h" /* Local includes in double quotes. */
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.Ed
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.Pp
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Macros are capitalized, parenthesized, and should avoid side-effects.
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If they are an inline expansion of a function, the function is defined
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all in lowercase, the macro has the same name all in uppercase. If the
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macro needs more than a single line, use braces. Right-justify the
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backslashes; it makes it easier to read.
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If the macro encapsulates a compound statement, enclose it in a
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.Dq Li do
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loop,
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so that it can safely be used in
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.Dq Li if
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statements.
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Any final statement-terminating semicolon should be
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supplied by the macro invocation rather than the macro, to make parsing easier
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for pretty-printers and editors.
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.Bd -literal -offset 0i
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#define MACRO(x, y) do { \e
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variable = (x) + (y); \e
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(y) += 2; \e
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} while(0)
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.Ed
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.Pp
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Enumeration values are all uppercase.
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.Bd -literal -offset 0i
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enum enumtype { ONE, TWO } et;
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.Ed
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.Pp
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When declaring variables in structures, declare them sorted by use, then
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by size, and then by alphabetical order. The first category normally
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doesn't apply, but there are exceptions. Each one gets its own line.
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Put a tab after the first word, i.e. use
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.Ql int^Ix;
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and
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.Ql struct^Ifoo *x; .
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.Pp
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Major structures should be declared at the top of the file in which they
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are used, or in separate header files if they are used in multiple
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source files. Use of the structures should be by separate declarations
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and should be "extern" if they are declared in a header file.
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.Bd -literal -offset 0i
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struct foo {
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struct foo *next; /* List of active foo */
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struct mumble amumble; /* Comment for mumble */
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int bar;
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};
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struct foo *foohead; /* Head of global foo list */
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.Ed
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.Pp
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Use
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.Xr queue 3
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macros rather than rolling your own lists, whenever possible. Thus,
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the previous example would be better written:
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.Bd -literal -offset 0i
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#include <sys/queue.h>
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struct foo {
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LIST_ENTRY(foo) link; /* Queue macro glue for foo lists */
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struct mumble amumble; /* Comment for mumble */
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int bar;
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};
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LIST_HEAD(, foo) foohead; /* Head of global foo list */
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.Ed
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.Pp
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Avoid using typedefs for structure types. This makes it impossible
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for applications to use pointers to such a structure opaquely, which
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is both possible and beneficial when using an ordinary struct tag.
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When convention requires a typedef, make its name match the struct
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tag. Avoid typedefs ending in
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.Dq Li \&_t ,
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except as specified in Standard C or by
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.Tn POSIX .
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.Bd -literal -offset 0i
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/* Make the structure name match the typedef. */
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typedef struct _bar {
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int level;
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} BAR;
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.Ed
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.Pp
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All functions are prototyped somewhere.
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.Pp
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Function prototypes for private functions (i.e. functions not used
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elsewhere) go at the top of the first source module. Functions
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local to one source module should be declared
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.Ql static .
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.Pp
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Functions used from other parts of the kernel are prototyped in the
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relevant include file.
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.Pp
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Functions that are used locally in more than one module go into a
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separate header file, e.g.
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.Pa extern.h .
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.Pp
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Only use the __P macro from the include file <sys/cdefs.h> if the source
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file in general is (to be) compilable with a K&R Old Testament compiler.
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Use of the __P macro in new code is discouraged, although modifications
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to existing files should be consistent with that file's conventions.
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.Pp
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In general code can be considered
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.Dq new code
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when it makes up about 50% or more of the file[s] involved. This is enough
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to break precedents in the existing code and use the current style guidelines.
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.Pp
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The kernel has a name associated with parameter types, e.g., in the kernel
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use:
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.Bd -literal -offset 0i
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void function(int fd);
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.Ed
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.Pp
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In header files visible to userland applications, prototypes that are
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visible must use either protected names or no names with the types. It
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is preferable to use protected names.
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e.g., use:
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.Bd -literal -offset 0i
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void function(int);
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.Ed
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.Pp
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or:
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.Bd -literal -offset 0i
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void function(int _fd);
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.Ed
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.Pp
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Prototypes may have an extra space after a tab to enable function names
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to line up:
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.Bd -literal -offset 0i
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static char *function(int _arg, const char *_arg2, struct foo *_arg3,
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struct bar *_arg4);
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static void usage(void);
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/*
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* All major routines should have a comment briefly describing what
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* they do. The comment before the "main" routine should describe
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* what the program does.
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*/
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int
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main(int argc, char *argv[])
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{
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long num;
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int ch;
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char *ep;
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.Ed
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.Pp
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For consistency, getopt should be used to parse options. Options
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should be sorted in the getopt call and the switch statement, unless
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parts of the switch cascade. Elements in a switch statement that
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cascade should have a FALLTHROUGH comment. Numerical arguments
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should be checked for accuracy. Code that cannot be reached should
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have a NOTREACHED comment.
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.Bd -literal -offset 0i
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while ((ch = getopt(argc, argv, "abn")) != -1)
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switch (ch) { /* Indent the switch. */
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case 'a': /* Don't indent the case. */
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aflag = 1;
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/* FALLTHROUGH */
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case 'b':
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bflag = 1;
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break;
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case 'n':
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num = strtol(optarg, &ep, 10);
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if (num <= 0 || *ep != '\e0') {
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warnx("illegal number, -n argument -- %s",
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optarg);
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usage();
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}
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break;
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case '?':
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default:
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usage();
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/* NOTREACHED */
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}
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argc -= optind;
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argv += optind;
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.Ed
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.Pp
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Space after keywords (if, while, for, return, switch). No braces are
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used for control statements with zero or only a single statement unless that
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statement is more than a single line in which case they are permitted.
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Forever loops are done with for's, not while's.
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.Bd -literal -offset 0i
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for (p = buf; *p != '\e0'; ++p)
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; /* nothing */
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for (;;)
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stmt;
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for (;;) {
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z = a + really + long + statement + that + needs +
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two lines + gets + indented + four + spaces +
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on + the + second + and + subsequent + lines;
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}
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for (;;) {
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if (cond)
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stmt;
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}
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if (val != NULL)
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val = realloc(val, newsize);
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.Ed
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.Pp
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Parts of a for loop may be left empty. Don't put declarations
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inside blocks unless the routine is unusually complicated.
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.Bd -literal -offset 0i
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for (; cnt < 15; cnt++) {
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stmt1;
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stmt2;
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}
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.Ed
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.Pp
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Indentation is an 8 character tab.
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Second level indents are four spaces.
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.Bd -literal -offset 0i
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while (cnt < 20)
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z = a + really + long + statement + that + needs +
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two lines + gets + indented + four + spaces +
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on + the + second + and + subsequent + lines.
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.Ed
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.Pp
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Do not add whitespace at the end of a line, and only use tabs
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followed by spaces
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to form the indentation. Do not use more spaces than a tab will produce
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and do not use spaces in front of tabs.
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.Pp
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Closing and opening braces go on the same line as the else.
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Braces that aren't necessary may be left out.
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.Bd -literal -offset 0i
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if (test)
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stmt;
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else if (bar) {
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stmt;
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stmt;
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} else
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stmt;
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.Ed
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.Pp
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No spaces after function names. Commas have a space after them. No spaces
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after
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.Sq \&(
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or
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.Sq \&[
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or preceding
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.Sq \&]
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or
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.Sq \&)
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characters.
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.Bd -literal -offset 0i
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if (error = function(a1, a2))
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exit(error);
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.Ed
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.Pp
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Unary operators don't require spaces, binary operators do. Don't
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use parentheses unless they're required for precedence or unless the
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statement is confusing without them. Remember that other people may
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confuse easier than you. Do YOU understand the following?
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.Bd -literal -offset 0i
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a = b->c[0] + ~d == (e || f) || g && h ? i : j >> 1;
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k = !(l & FLAGS);
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.Ed
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.Pp
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Exits should be 0 on success, or according to the predefined
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values in
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.Xr sysexits 3 .
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.Bd -literal -offset 0i
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exit(EX_OK); /*
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* Avoid obvious comments such as
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* "Exit 0 on success."
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*/
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}
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.Ed
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.Pp
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The function type should be on a line by itself
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preceding the function.
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.Bd -literal -offset 0i
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static char *
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function(int a1, int a2, float fl, int a4)
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{
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.Ed
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.Pp
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When declaring variables in functions declare them sorted by size,
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then in alphabetical order; multiple ones per line are okay.
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Declaring functions inside functions is not recommended, since their
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linkage scope is always global. If a line overflows reuse the type
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keyword.
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.Pp
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Be careful to not obfuscate the code by initializing variables in
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the declarations. Use this feature only thoughtfully.
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DO NOT use function calls in initializers!
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.Bd -literal -offset 0i
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struct foo one, *two;
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double three;
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int *four, five;
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char *six, seven, eight, nine, ten, eleven, twelve;
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four = myfunction();
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.Ed
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.Pp
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Do not declare functions inside other functions; ANSI C says that
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such declarations have file scope regardless of the nesting of the
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declaration. Hiding file declarations in what appears to be a local
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scope is undesirable and will elicit complaints from a good compiler.
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.Pp
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Casts and sizeof's are not followed by a space. Note that
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.Xr indent 1
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does not understand this rule.
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.Pp
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NULL is the preferred null pointer constant. Use NULL instead of
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(type *)0 or (type *)NULL in contexts where the compiler knows the
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type, e.g., in assignments. Use (type *)NULL in other contexts,
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in particular for all function args. (Casting is essential for
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variadic args and is necessary for other args if the function prototype
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might not be in scope.)
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Test pointers
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against NULL, e.g., use:
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.Bd -literal -offset 0i
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(p = f()) == NULL
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.Ed
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.Pp
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not:
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.Bd -literal -offset 0i
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!(p = f())
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.Ed
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.Pp
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Don't use '!' for tests unless it's a boolean, e.g. use
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.Bd -literal -offset 0i
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if (*p == '\e0')
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.Ed
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.Pp
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not
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.Bd -literal -offset 0i
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if (!*p)
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.Ed
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.Pp
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Routines returning void * should not have their return values cast
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to any pointer type.
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.Pp
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Use
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.Xr err 3
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or
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.Xr warn 3 ,
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don't roll your own!
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.Bd -literal -offset 0i
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if ((four = malloc(sizeof(struct foo))) == NULL)
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err(1, (char *)NULL);
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if ((six = (int *)overflow()) == NULL)
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errx(1, "Number overflowed.");
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return (eight);
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}
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.Ed
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.Pp
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Old-style function declarations look like this:
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.Bd -literal -offset 0i
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static char *
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function(a1, a2, fl, a4)
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int a1, a2; /* Declare ints, too, don't default them. */
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float fl; /* Beware double vs. float prototype differences. */
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int a4; /* List in order declared. */
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{
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.Ed
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.Pp
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Use ANSI function declarations unless you explicitly need K&R compatibility.
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.Pp
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Variable numbers of arguments should look like this.
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|
.Bd -literal -offset 0i
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|
#include <stdarg.h>
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|
|
|
void
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|
vaf(const char *fmt, ...)
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|
{
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|
va_list ap;
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|
|
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va_start(ap, fmt);
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STUFF;
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va_end(ap);
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/* No return needed for void functions. */
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}
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|
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static void
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usage()
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{
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|
/* Insert an empty line if the function has no local variables. */
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|
.Ed
|
|
.Pp
|
|
Use
|
|
.Xr printf 3 ,
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|
not fputs/puts/putchar/whatever; it's faster and usually cleaner, not
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|
to mention avoiding stupid bugs.
|
|
.Pp
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|
Usage statements should look like the manual pages. Options w/o
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|
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
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|
are specified, followed by optional arguments in the order they
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|
are specified. A bar
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|
.Pq Sq \&|
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|
separates either-or options/arguments,
|
|
and multiple options/arguments which are specified together are
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|
placed in a single set of braces.
|
|
.Pp
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|
.Bd -ragged -offset 0.3i
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|
"usage: f [-ade] [-b b_arg] [-m m_arg] req1 req2 [opt1 [opt2]]\en"
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|
"usage: f [-a | -b] [-c [-de] [-n number]]\en"
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|
.Ed
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|
.Bd -literal -offset 0i
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|
(void)fprintf(stderr, "usage: f [-ab]\en");
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exit(1);
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}
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.Ed
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|
.Pp
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|
New core kernel code should be reasonably compliant with the style guides.
|
|
The guidelines for third-party maintained modules and device drivers are more
|
|
relaxed but at a minimum should be internally consistent with their style.
|
|
.Pp
|
|
Stylistic changes (including whitespace changes) are hard on the source
|
|
repository and are to be avoided without good reason. Code that is
|
|
approximately KNF compliant in the repository must not diverge from
|
|
compliance.
|
|
.Pp
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|
Whenever possible, code should be run through a code checker
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|
(e.g., "gcc -Wall" or xlint(1)) and produce minimal warnings.
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|
|
.Sh SEE ALSO
|
|
.Xr indent 1 ,
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.Xr err 3 ,
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|
.Xr sysexits 3 ,
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|
.Xr warn 3
|
|
.Sh HISTORY
|
|
This man page is largely based on the src/admin/style/style file from
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|
the
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|
.Tn BSD
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|
4.4-Lite2 release, with updates to reflect the current practice and
|
|
desire of the
|
|
.Tn FreeBSD
|
|
project.
|