81 lines
2.9 KiB
Groff
81 lines
2.9 KiB
Groff
.\" $NetBSD: __FPTRCAST.3,v 1.2 2019/11/11 11:06:27 wiz Exp $ $
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.\"
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.\" Copyright (c) 2019 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 Christos Zoulas
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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 October 17, 2013
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.Dt __FPTRCAST 3
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.Os
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.Sh NAME
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.Nm __FPTRCAST
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.Nd function pointer cast
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.Sh SYNOPSIS
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.In sys/cdefs.h
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.Ft ftype
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.Fn __FPTRCAST ftype fname
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.Sh DESCRIPTION
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The
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.Fn __FPTRCAST
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macro can be used to silence warnings produced by certain compilers when
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converting from one function pointer type to another.
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The
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.Fa ftype
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argument is the function pointer type to which to cast the function
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pointer in
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.Fa fname .
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.Pp
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This cast should be used sparingly and it is typically used in the following
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situations:
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.Bl -bullet -offset indent -compact
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.It
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We know that the function prototypes don't match at all, but we don't care
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because we point it to a function that does not take arguments and returns
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an error.
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.It
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We only care about the first few arguments and we don't care about the rest.
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.It
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We don't care about the return value, we ignore it anyway.
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.El
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.Sh IMPLEMENTATION NOTES
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This macro is implemented by using an intermediate
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.Em void *
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cast.
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.Sh SEE ALSO
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.Xr cc 1 ,
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.Xr cdefs 3
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.Sh CAVEATS
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Use of this macro can hide valid errors, and its usage is not recommended
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unless there is a well-thought reason for a cast.
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As a general guideline, don't use this macro inside other macros because
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it will hide cases where the user of the original macro accidentally used
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an incorrect function pointer.
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.Pp
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Use of this macro is non-portable; this is part of the implementation
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namespace and should only be used in
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.Nx
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code.
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