Re: [boost] [regex] number of back references

From: Lorenzo Bettini (bettini_at_[hidden])
Date: 2007-04-28 14:41:08

Eric Niebler wrote:
> Lorenzo Bettini wrote:
>> Eric Niebler wrote:
>>> John Maddock wrote:
>>>> Lorenzo Bettini wrote:
>>>>> Hi
>>>>>
>>>>> is there any plan to support more than 9 back references in the regex
>>>>> library?
>>>> You can have as many marked sub-expressions as you want, and refer to them 
>>>> in the match_results structure once you have a match.  What you can't do at 
>>>> present is have a true back-reference say \12 in your expression.
>>> You could use xpressive, which handles this case.
>> OK, thanks, I'll take a look at it...  is xpressive compatible with
>> boost::regex expressions?
> 
> Boost.Regex and Boost.Xpressive accept the same basic regex syntax. 
> Xpressive doesn't yet support collating elements (eg., [.ae.]) and 
> equivalence classes (eg., [=a=]).

OK, thanks...  probably I wouldn't need these features at the moment...

by the way, I use regular expressions for this
http://www.gnu.org/software/src-highlite

> 
> I should also say that as a result of your inquiry, I found an 
> off-by-one error in Xpressive's handling of back-references over 9. If 
> you want to access back-ref \12, you'll need 13 captures in your 
> expression. Darn. It might be too late to fix for 1.34, but I'll patch 
> the archive in the Vault. It's already fixed in HEAD.
> 

by the way, I noticed that I don't have any debian boost package for
xpressive... it's been part of boost since when?

is it made only of headers, or also of a library?

thanks again
        Lorenzo

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Lorenzo Bettini, PhD in Computer Science, DSI, Univ. di Firenze
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