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From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: IsUnsigned() function (retiring injured)
Message-ID: <25836@mimsy.umd.edu>
Date: 2 Aug 90 05:46:49 GMT
References: <1990Jul27.161339.14712@kfw.COM> <8118@ncar.ucar.edu> <621@.tetrauk.UUCP>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 20

In article <621@.tetrauk.UUCP> rick@.tetrauk.UUCP (Rick Jones) writes:
>Perhaps I finally understand the ANSII promotion rules at last!

Probably not. :-)  (Incidentally, `ANSI' has only one `I'; it is
`ASCII' that has two.)

Actually, the rule is fairly easy to state:  `In ANSI C, when an
unsigned type is promoted% to some other type, it becomes signed
(without changing value) if and only if the new type is actually
bigger.'  In practise, this means that you have to know whether
sizeof(short) < sizeof(int) and whether sizeof(char) < sizeof(int).

Alternatively, never let values promote without using a cast to
a non-promoting type; this avoids the problem entirely.
-----
% `Promotion' is not the same as `conversion' or `assignment'.
  See the standard (X3.159-1989) for an exact description.
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@cs.umd.edu	Path:	uunet!mimsy!chris