.\" $NetBSD: cdefs.3,v 1.4 2013/10/27 10:05:15 apb Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jukka Ruohonen.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
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.Dd April 8, 2011
.Dt CDEFS 3
.Os
.Sh NAME
.Nm cdefs
.Nd common definitions and macros
.Sh SYNOPSIS
.In sys/cdefs.h
.Sh DESCRIPTION
The
.In sys/cdefs.h
header includes some common definitions and macros
typical to the C language conventions of
.Nx .
Among these are:
.Bl -bullet -offset indent
.It
Certain C language properties and definitions that
are versioned according to the support in compilers.
Examples include the
.Em __func__
keyword and the
.Em restrict
type qualifier from
.Tn C99 .
.It
Macros and definitions specific to compilers, preprocessors, and linkers; see
.Xr __CONCAT 3 ,
.Xr __UNCONST 3 ,
.Xr __USE 3 ,
.Xr __insn_barrier 3 ,
and
.Xr attribute 3 .
.It
Utility macros provided for convenience; see
.Xr __arraycount 3
and
.Xr bits 3 .
.El
.Pp
The header also contains the
.Fn __RCSID
and
.Fn __KERNEL_RCSID
macros used for version control system
.Pq Tn VCS
identifiers.
Thus, all
.Nx
source code files typically include
.In sys/cdefs.h ,
included as the first thing right after any possible copyright texts;
.Bd -literal -offset indent
/*-
 * Copyright (c) 1984 John Doe
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms,
 * with or without modification, are permitted.
 */

#include <sys/cdefs.h>
__RCSID("$NetBSD: cdefs.3,v 1.4 2013/10/27 10:05:15 apb Exp $");
.Ed
.Pp
It is possible to identify the
.Tn RCS
keyword strings by using
.Xr ident 1 .
.Sh SEE ALSO
.Xr ident 1 ,
.Xr param 3 ,
.Xr stddef 3 ,
.Xr types 3 ,
.Xr c 7
.Sh HISTORY
The
.In sys/cdefs.h
header was originally imported from
.Bx 386 .