problematic document for isascii(3)

Eric Blake
Thu May 23 14:25:00 GMT 2013

On 05/23/2013 07:21 AM, ntysdd wrote:
> Hi,
> I found something buggy in the document.
> The doc says "`isascii' is ANSI C", but it isn't.
> It is a BSD extension.

Actually, it is also POSIX, but you are correct that it is not C.

> Also the doc for isdigit says
> "It is defined only when `isascii'(C) is true or C is EOF."

This is a lie; isascii(128) returns false, but isdigit(128) is well=defined.

> But isdigit is ANSI C so it should not rely on isascii.
> And after reading the ansi draft, I think isdigit is defined
> for anything representable as an unsigned char (plus EOF).

Correct, that is also the POSIX wording:

> By the way, the doc says isdigit is a macro using a table.
> I don't think it need be implemented in this way because
> something like '0' <= C && C<='9' is good enough.

That's still a table lookup, of sorts.  The implementation can do
whatever it wants under the hood, as long as the as-if rule is honored
and you get the same results.

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library

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