Notes on the ANSI standard

[Henry Spencer]

> Section 4.1.3 states:
> 
>    "With one exception, a member of a union object may not be
>    inspected unless the value of the object has been assigned
>    using that same member."
> 
> HOLY <censored>!!  Whatever happened to overlaying values of differing
> types?  One of the more handy uses of unions is overlaying bitfields
> with an integer so that the bits can be twiddled individually, but the
> integer can be used for block operations on all the bits.  I've also
> used similar techniques for decoding bit fields of devices like a
> Summagraphic Bitpad, or several mouses.

Unions were intended as a storage-allocation-control mechanism, not as
a way to do type cheating.  The orthodox way to do the latter is casts.

Incidentally, using integers and bit operations (yes, I know it's ugly)
is probably more portable than bitfields.  Believe it or not.  Partly
because a good many compilers botch bitfields, partly because things
like the bit allocation of bitfields are very compiler-dependent.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry