1.\" $NetBSD: __FPTRCAST.3,v 1.2 2019/11/11 11:06:27 wiz Exp $ $ 2.\" 3.\" Copyright (c) 2019 The NetBSD Foundation, Inc. 4.\" All rights reserved. 5.\" 6.\" This code is derived from software contributed to The NetBSD Foundation 7.\" by Christos Zoulas 8.\" 9.\" Redistribution and use in source and binary forms, with or without 10.\" modification, are permitted provided that the following conditions 11.\" are met: 12.\" 1. Redistributions of source code must retain the above copyright 13.\" notice, this list of conditions and the following disclaimer. 14.\" 2. Redistributions in binary form must reproduce the above copyright 15.\" notice, this list of conditions and the following disclaimer in the 16.\" documentation and/or other materials provided with the distribution. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 19.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 20.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 21.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 22.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 23.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 24.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 25.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 26.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 27.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 28.\" POSSIBILITY OF SUCH DAMAGE. 29.\" 30.Dd October 17, 2013 31.Dt __FPTRCAST 3 32.Os 33.Sh NAME 34.Nm __FPTRCAST 35.Nd function pointer cast 36.Sh SYNOPSIS 37.In sys/cdefs.h 38.Ft ftype 39.Fn __FPTRCAST ftype fname 40.Sh DESCRIPTION 41The 42.Fn __FPTRCAST 43macro can be used to silence warnings produced by certain compilers when 44converting from one function pointer type to another. 45The 46.Fa ftype 47argument is the function pointer type to which to cast the function 48pointer in 49.Fa fname . 50.Pp 51This cast should be used sparingly and it is typically used in the following 52situations: 53.Bl -bullet -offset indent -compact 54.It 55We know that the function prototypes don't match at all, but we don't care 56because we point it to a function that does not take arguments and returns 57an error. 58.It 59We only care about the first few arguments and we don't care about the rest. 60.It 61We don't care about the return value, we ignore it anyway. 62.El 63.Sh IMPLEMENTATION NOTES 64This macro is implemented by using an intermediate 65.Em void * 66cast. 67.Sh SEE ALSO 68.Xr cc 1 , 69.Xr cdefs 3 70.Sh CAVEATS 71Use of this macro can hide valid errors, and its usage is not recommended 72unless there is a well-thought reason for a cast. 73As a general guideline, don't use this macro inside other macros because 74it will hide cases where the user of the original macro accidentally used 75an incorrect function pointer. 76.Pp 77Use of this macro is non-portable; this is part of the implementation 78namespace and should only be used in 79.Nx 80code. 81