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