CTRL(x)

[Gregory Smith]

In article <4880 at brl-smoke.ARPA> kb5mu at NOSC.ARPA writes:
>>But. . .is there a way to write an ANSI cpp version of
>>        #define CTRL(c)
>
>I don't have an ANSI cpp handy (does anybody?), so I can't test
>this, but how about using the ANSI invention of # for "string-izing":
>        #define CTRL(c) (#c[0] & 037)
>This should turn
>        CTRL(z)
>into
>        ("z"[0] & 037)
>which would get what you wanted, except that relatively stupid
>compilers might allocate storage for the string literal "z".

It's worse than that. "z"[0] is *("z"), and unary * is not allowed
in constant expressions. So ALL compilers would allow storage for "z"
and then generate code to read that storage at run-time.
Of course, ``case CTRL(c):'' wouldn't work either.

You don't expect C compilers to pull constants out of string literals,
do you?
[ I don't have an Ansi draft, so as far as I know there may be a rule
saying that constant expressions may contain string literals indexed by
constants. But I doubt it].

-- 
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Greg Smith     University of Toronto      UUCP: ..utzoo!utcsri!greg