91 lines
2.8 KiB
Groff
91 lines
2.8 KiB
Groff
.\" $NetBSD: __UNCONST.3,v 1.1 2010/03/01 13:44:09 jruoho Exp $
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.\"
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.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" This code is derived from software contributed to The NetBSD Foundation
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.\" by Jukka Ruohonen.
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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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd February 28, 2010
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.Os
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.Dt __UNCONST 3
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.Sh NAME
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.Nm __UNCONST
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.Nd compile time cast-away macro
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.Sh SYNOPSIS
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.In sys/cdefs.h
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.Ft void
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.Fn __UNCONST x
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.Ft void
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.Fn __UNVOLATILE x
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.Sh DESCRIPTION
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The
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.Fn __UNCONST
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macro can be used to omit warnings produced by certain compilers when
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a pointer declared with the
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.Em const
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type qualifier is being passed to a function without such qualifier.
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In the same vein, the
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.Fn __UNVOLATILE
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macro can be used to omit warnings related to the
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.Em volatile
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type qualifier.
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.Pp
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.Sh IMPLEMENTATION NOTES
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Both macros are implemented by explicitly using
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.Em unsigned long
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instead of
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.Em intptr_t ,
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a signed type guaranteed to hold a pointer.
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.Sh EXAMPLES
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The following example demonstrates a possible usage of
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.Fn __UNCONST :
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.Bd -literal -offset indent
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const char *str = "/dev/null";
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api_function(__UNCONST(str));
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\&...
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static void
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api_function(char *str)
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{
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\&...
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.Ed
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.Sh CAVEATS
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Both macros should be used with care because these can hide valid errors.
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A typical use case for
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.Fn __UNCONST
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involve an
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.Tn API
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that does not follow the so-called ``const correctness''
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even if it would be appropriate.
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Valid use cases of
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.Fn __UNVOLATILE
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include passing a volatile pointer to
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.Xr memset 3 .
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.Sh SEE ALSO
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.Xr cc 1
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