Re: [boost] [xpressive] Concatenating two regular expressions into one?

Subject: Re: [boost] [xpressive] Concatenating two regular expressions into one?
From: Eric Niebler (eric_at_[hidden])
Date: 2012-03-14 21:33:02

On 3/13/2012 3:18 PM, Robert Dailey wrote:
> I have the following function:
> 
>     bool MimeDocument::GetMimeHeaderData( PMIMEENTITY entity,
> MimeHeaderData& header_data )
>     {
>         bool success = false;
> 
>         std::string headers;
>         GetMimeEntityData( entity, MIME_ENTITY_DATA_HEADERS, headers );
> 
>         using namespace boost::xpressive;
> 
>         sregex content_disposition_re =
>             icase("Content-Disposition:") >> +_s >> (s1=!as_xpr("inline;"))
>             >> -*_ >> "size=" >> (s2=+_d) >> ';'
>             ;
> 
>         sregex content_id_re =
>             icase("Content-ID:") >> +_s >> '<' >> (s1=+_) >> '>'
>             ;
> 
>         smatch what;
>         if( regex_search( headers, what, content_disposition_re ) ) {
>             header_data.is_inline = what[1] == "inline;";
>             header_data.size = boost::lexical_cast<unsigned>( what[2] );
>             success = true;
>         }
> 
>         if( regex_search( headers, what, content_id_re ) ) {
>             header_data.content_id = what[1];
>             success = true;
>         }
> 
>         return success;
>     }
> 
> Right now I use 2 sregex objects and search the MIME headers twice to find
> 2 different lines. Ideally I'd like to just use 1 regex and combine them,
> but I need to then somehow make it search between all lines, and then the
> order in which Content-Distribution and Content-ID appear in the headers
> may vary. Is it best to keep them separated like this, or can I concatenate
> the regular expressions into 1?

I could certainly come up with a way to combine them, I don't see a
particular need. My solution would be more complicated than what you
have shown. Is there a particular reason why you feel the code above is
insufficient?

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