Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!cs.utexas.edu!uunet!dino!atanasoff!hascall
From: hascall@atanasoff.cs.iastate.edu (John Hascall)
Newsgroups: comp.lang.c
Subject: Re: "address" of a bitfield
Message-ID: <1226@atanasoff.cs.iastate.edu>
Date: 18 Jul 89 15:22:52 GMT
References: <2840@blake.acs.washington.edu> <1989Jul17.212555.24509@utzoo.uucp>
Reply-To: hascall@atanasoff.cs.iastate.edu.UUCP (John Hascall)
Organization: Iowa State Univ. Computation Center
Lines: 23

In article <utzoo.uucp> henry@utzoo.uucp (Henry Spencer) writes:
>In article <@blake.acs.washington.edu> wiml@blake.UUCP (William Lewis) writes:
 
>>  which would assign to 'start' the (char *) pointing to the start of the
>>bitfield, to 'offset' the number of bits into the char the bitfield starts,
>>and to 'width' the width of the bitfield in bits...
>>    Does anyone know of an even semi-portable way to do this? ...
 
>Can't be done -- the packing of bitfields into words/chars/whatever is
>highly machine-specific (even the order, left-to-right or right-to-left,
>varies) and the information is not available to the program.

    But it is available to the compiler!  Which is what I think Mr. Lewis
    was thinking of--that it be handled like the "sizeof" operator.

    It seems like useful information, but perhaps separate operators would
    be more convenient:

	 bit_sizeof(foo)
	 bit_offsetof(foo)
	 bit_baseof(foo)

    John Hascall  /  ISU Comp Center  /  Ames IA