.\"	$NetBSD: __UNCONST.3,v 1.7 2013/10/17 20:43:49 wiz Exp $
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.\" by Jukka Ruohonen.
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.Dd October 17, 2013
.Dt __UNCONST 3
.Os
.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
operating with pointers declared with the
.Em const
type qualifier in a context without such qualifier.
Examples include passing a pointer declared with the
.Em const
qualifier to a function without such qualifier,
and variable assignment from a
.Em const
pointer to a non-const pointer.
In the same vein, the
.Fn __UNVOLATILE
macro can be used to exclude warnings related to the
.Em volatile
type qualifier.
.Sh IMPLEMENTATION NOTES
These macros are implemented by explicitly using
.Em unsigned long
instead of
.Em intptr_t ,
a signed type guaranteed to hold a pointer.
.Sh SEE ALSO
.Xr cc 1 ,
.Xr cdefs 3
.Sh CAVEATS
As both macros may hide valid errors, their usage is not recommended
unless there is a well-thought reason for a cast.
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
.Em volatile
pointer to
.Xr memset 3 .
.Pp
Use of this macro is non-portable; this is part of the implementation
namespace and should only be used in
.Nx
code.