From: Josef 'Jupp' SCHUGT <jupp@...>
Date: 2006-02-14T07:28:23+09:00
Subject: Re: Scanning a string for decimal numbers

Hi!

At Sun, 12 Feb 2006 08:12:47 +0900, Jeppe Jakobsen wrote:
> 
> Will that expression include both integers and decimal numbers?

[-+]?([1-9]\d*(\,[0-9]+)?)|(0(\,[0-9]+)?)

has two parts:

[-+]?
([1-9]\d*(\,[0-9]+)?)|(0(\,[0-9]+)?)


The first one is an optional sign. The second one is an alternative
between to two cases:

[1-9]\d*(\,[0-9]+)?
0(\,[0-9]+)?

Let's first consider the first case

[1-9]\d*(\,[0-9]+)?

It has two parts, namely

[1-9]\d*
(\,[0-9])?

The first part by itself covers all integers larger than zero. The
overall expression additionally covers all floating point numbers
larger than 1.

Now the second case

0(\,[0-9]+)?

This one covers zero and all decimal numbers larger than 0 and smaller
than 1.

The regex I provided intentionally supports none of

[+-],\d+
[+-]0+\d+

You may as well use the shorter version

[-+]?(([1-9]\d*(\,\d+)?)|(0(\,\d+)?))

Wait a moment, I am not sure if that is correct. To be on the safe
side I'd rather use one of these where anything that follows the
optional sign has been put into another pair of parentheses:

[-+]?(([1-9]\d*(\,[0-9]+)?)|(0(\,[0-9]+)?))
[-+]?((([1-9]\d*(\,\d+)?)|(0(\,\d+)?)))

I am one of those guys who sometime run out of placeholders when doing
search and replace in vim (which has nine of them).

Josef 'Jupp' Schugt
-- 
Let the origin be the middle of the earth, p(x,r) be the probability
density for finding person x at distance r. Make sure that a permanent
solution of int_0^R p(x,r) dr < 1 exists for R being the instantanous
value of the distance between earth and mars.