.\"	$NetBSD: __UNCONST.3,v 1.1 2010/03/01 13:44:09 jruoho Exp $
.\"
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.\" by Jukka Ruohonen.
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.Dd February 28, 2010
.Os
.Dt __UNCONST 3
.Sh NAME
.Nm __UNCONST
.Nd compile time cast-away macro
.Sh SYNOPSIS
.In sys/cdefs.h
.Ft void
.Fn __UNCONST x
.Ft void
.Fn __UNVOLATILE x
.Sh DESCRIPTION
The
.Fn __UNCONST
macro can be used to omit warnings produced by certain compilers when
a pointer declared with the
.Em const
type qualifier is being passed to a function without such qualifier.
In the same vein, the
.Fn __UNVOLATILE
macro can be used to omit warnings related to the
.Em volatile
type qualifier.
.Pp
.Sh IMPLEMENTATION NOTES
Both macros are implemented by explicitly using
.Em unsigned long
instead of
.Em intptr_t ,
a signed type guaranteed to hold a pointer.
.Sh EXAMPLES
The following example demonstrates a possible usage of
.Fn __UNCONST :
.Bd -literal -offset indent
const char *str = "/dev/null";

api_function(__UNCONST(str));

\&...

static void
api_function(char *str)
{
	\&...

.Ed
.Sh CAVEATS
Both macros should be used with care because these can hide valid errors.
A typical use case for
.Fn __UNCONST
involve an
.Tn API
that does not follow the so-called ``const correctness''
even if it would be appropriate.
Valid use cases of
.Fn __UNVOLATILE
include passing a volatile pointer to
.Xr memset 3 .
.Sh SEE ALSO
.Xr cc 1