[TUHS] X and NeWS history (long)

Warner Losh imp at bsdimp.com
Fri Sep 15 01:12:31 AEST 2017


On Thu, Sep 14, 2017 at 6:30 AM, Richard Tobin <richard at inf.ed.ac.uk> wrote:

> > I really kind of liked that toolkit, it was all key/value like so:
> >
> >         panel = xv_create(
> >           frame, PANEL,
> >             XV_WIDTH, WIDTH,
> >           XV_HEIGHT, 30,
> >             PANEL_LAYOUT, PANEL_HORIZONTAL,
> >             XV_SHOW, FALSE,
> >           NULL);
> >
> > So the order of the args didn't really matter, I think the first one
> > maybe did because that was the parent but not sure, the rest could
> > be any order you wanted.  Pretty simple.
>
> The first two were fixed; the prototype was
>
>   Xv_object xv_create (Xv_opaque owner, Xv_pkg *pkg, ...);
>
> The keywords (XV_WIDTH etc) contained a bitfield encoding the type and
> cardinality of the value argument(s) so that the argument list could
> be traversed without knowing every package's keywords.
>
> Using NULL as the terminating argument looks unportable.


It turned out to be portable enough. And no worse than calloc dependencies
in the base X11 library (which assumes that the address used when the
integer 0 is assigned to a pointer has no bits set). The only other
assumption was that pointers and ints were passed the same way, and that
whatever NULL expanded to was at least as long as an int.

So, yes this wouldn't work on a system whose null-pointer representation
contained bits set, but that was already an assumption of X11...

Warner
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