Re: Command Languages Versus Programming Languages

cross@spitfire.i.gajendra.net (Dan Cross) writes:

Rainer Weikusat  <rweikusat@talktalk.net> wrote:

Janis Papanagnou <janis_papanagnou+ng@hotmail.com> writes:
>
[...]
>

Personally I think that writing bulky procedural stuff for something
like [0-9]+ can only be much worse, and that further abbreviations
like \d+ are the better direction to go if targeting a good interface.
YMMV.

>
Assuming that p is a pointer to the current position in a string, e is a
pointer to the end of it (ie, point just past the last byte) and -
that's important - both are pointers to unsigned quantities, the 'bulky'
C equivalent of [0-9]+ is
>
while (p < e && *p - '0' < 10) ++p;
>
That's not too bad. And it's really a hell lot faster than a
general-purpose automaton programmed to recognize the same pattern
(which might not matter most of the time, but sometimes, it does).

>
It's also not exactly right.  `[0-9]+` would match one or more
characters; this possibly matches 0 (ie, if `p` pointed to
something that wasn't a digit).

The regex won't match any digits if there aren't any. In this case, the
match will fail. I didn't include the code for handling that because it
seemed pretty pointless for the example.