Preprocessor macro to quote its argument

[Henry Spencer]

In article <21594 at grebyn.com> ckp at grebyn.UUCP (Checkpoint Technologies) writes:
>Why can't this work?
>#define CTRL(ch) ((* #ch) - 64)
>Now, I know this *could* be a constant expression...

3.4 says that the value of an object may not be accessed by a `*' operator
in a constant expression, so this isn't a constant expression in a portable
sense.  However, it is not a constraint violation, so the compiler is not
*required* to complain about it, and 3.4 does explicitly authorize compilers
to accept "other forms" of constant expression.  So your comment is correct:
it *could be* a constant expression, but isn't dependably one.  Alas, one
use of the `CTRL(D)' hack is in case labels, where constant expressions are
required.
-- 
Committees do harm merely by existing. | Henry Spencer at U of Toronto Zoology
                       -Freeman Dyson  |  henry at zoo.toronto.edu   utzoo!henry