Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!elf115!rec
From: rec@elf115.uu.net (Roger Critchlow)
Newsgroups: comp.lang.c
Subject: Re: "address" of a bitfield
Summary: Sorry, no solution
Message-ID: <158@elf115.uu.net>
Date: 17 Jul 89 16:04:36 GMT
References: <2840@blake.acs.washington.edu>
Organization: ELF, Sea Cliff, NY
Lines: 27

In article <2840@blake.acs.washington.edu>, wiml@blake.acs.washington.edu (William Lewis) writes:
> 
> [reasonable reasons for wanting the address of a bitfield]
>
>     Does anyone know of an even semi-portable way to do this? Or, if
> there is no portable way, a way that works with Mark Williams C on
> a MSDOS machine? 

There isn't currently any way to do this with the Mark Williams compiler,
and there is no way to do this defined by the dpANS.

But, I note that the result of the dpANS offsetof() macro is undefined
when applied to a bitfield member, and if a compiler treated this macro
with special care it might be possible to provide the necessary infor-
mation for those who need it.

One possibility would be for offsetof(type, bit-field-member) to generate
a triple of constants:

  bit_offset_constant, bit_width_constant, byte_offset_constant

which could be plugged into a user defined function call argument list to
a bit field pointer constructor.

Does anyone see any problems with this as an extension to dpANS?

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