Re: C++ way to convert ASCII digits to Integer?

From:

"Alf P. Steinbach" <alfps@start.no>

Newsgroups:

comp.lang.c++

Date:

Sun, 31 May 2009 16:52:01 +0200

Message-ID:

<gvu5lu$bjm$1@news.eternal-september.org>

* osmium:

James Kanze wrote:

On May 29, 3:08 pm, Gerhard Fiedler <geli...@gmail.com> wrote:

James Kanze wrote:

(Given that ASCII is for all intents and purposes dead, it's
highly unlikely that they really want ASCII.)

I'm not sure, but I think in the USA there is quite a number
of programmers who don't think beyond ASCII when thinking of
text manipulation.

In just about every country, there are quite a number of
programmers who don't think:-). The fact remains that the
default encoding used by the system, even when configured for
the US, is not ASCII. Even if you're not "thinking" beyond
ASCII, your program must be capable of reading non-ASCII
characters (if only to recognize them and signal the error).

Is it your point that an ASCII compliant environment would have to signal an
error if the topmost bit in a byte was something other than 0?

I think James is perhaps referring to routines like isdigit family.

Some of them take int argument and have UB if the argument value is outside
0...(unsigned char)(-1).

So with most implementations you get UB if you simply pass a char directly as
argument and that char is beyond ASCII range, because then it will be negative.

Or do you
have something else in mind? I don't have the *actual* ASCII standard
available but I would be surprised if that was expressed as a *requirement*.

See above.

After all, the people that wrote the standard were well aware that there was
no such thing as a seven-bit machine.

On the contrary, the seven bit nature of ASCII was to facilitate communication
over e.g. serial links with software parity check, where each byte was
effectively seven bits (since one bit was used for parity).

Cheers & hth.,

- Alf

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