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

From:
blargg.ei3@gishpuppy.com (blargg)
Newsgroups:
comp.lang.c++
Date:
Wed, 27 May 2009 14:05:19 -0500
Message-ID:
<blargg.ei3-2705091405200001@192.168.1.4>
blargg wrote:

andreas.koestler wrote:

On May 27, 9:18?am, "Peter Olcott" <NoS...@SeeScreen.com> wrote:

I remember that there is a clean C++ way to do this [convert
ASCII digits to Integer], but, I forgot what it was.


I don't know what you mean by 'clean C++ way' but one way to do it is:

int ascii_digit_to_int ( const char asciidigit ) {
  if ( asciidigit < '0' ||
       asciidigit > '9' ) {
    throw NotADigitException();
  }
  return (int) asciidigit - 48; // 48 => '0'
}

[...]

Not if the machine doesn't use ASCII; only a function like yours above
is fully portable.


Whoops, that's wrong too, as the above function uses '0' and '9', which
won't be ASCII on a non-ASCII machine. So the above should really use 48
and 57 in place of those character constants, to live up to its name.
Otherwise, on a machine using ASCII, it'll work, but on another, it'll be
broken and neither convert from ASCII nor the machine's native character
set!

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