Re: [Boost-users] Newbie Xpressive Help Needed

Subject: Re: [Boost-users] Newbie Xpressive Help Needed
From: Eric Niebler (eric_at_[hidden])
Date: 2010-02-24 22:42:22

On 2/25/2010 1:42 PM, Timothy Sassone wrote:
> I'm new to both boost and Xpressive, but I've worked with regex before.
> I've been able figure most of it out from the Xpressive user guide,
> but I'm having some trouble with a particular expression.
<snip>
> since the date of death is sometimes completely
> absent, I need some way to get the number if it's there, and skip it
> otherwise.  From what I understand, I'll need to use the lookahead or
> lookbehind constructs
<snip>

It's much simpler than that. You want an optional quantifier.

> Here's what I'm using to parse up through the date of birth...
> mark_tag RU_Name(1), RU_Birth(2), RU_Death(3), RU_ReignBegin(4),
> RU_Line(5), RU_Married(6);
> sregex Reg_Ruler = "  [*] " >> ( RU_Name = +(+_w|_s) ) >> "(b." >>
> (RU_Birth = (+(_d)|"???"));

  ... >> !("d." >> (RU_Death = +_d)) >> ...

The '!' makes the sub-expression match 1 or 0 times.

After the regex_match, you can check the match_results to see if 
RU_Death participated in the match like:

   if (results[RU_Death].matched)
     // ... results[RU_Death] contains a date of death.

> Any help would be much appreciated, and a link to a decent tutorial to
> help me with Xpressive in general would be even better.

The decent tutorial on xpressive is the users' guide. Or does that not 
qualify as "decent"? Ahem. ;-)

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com