Re: [Boost-users] Get All Words Offset in String using Boost regex

Subject: Re: [Boost-users] Get All Words Offset in String using Boost regex
From: S Nagre (snagre.mumbai_at_[hidden])
Date: 2012-01-06 12:12:35

Many Thanks Anthony , Your version of code works much better than mine..

Thanks
Subhash

On Fri, Jan 6, 2012 at 2:25 AM, Anthony Foiani <tkil_at_[hidden]> wrote:

>
> S Nagre <snagre.mumbai_at_[hidden]> writes:
>
> >        std::string escapeChar = "\\" ;
> >        std::string bChar = "b";
> >        std::string dotChar = ".";
> >
> >        std::string findWordInStr = escapeChar + bChar + dotChar +
> >    escapeChar + bChar;
>
> This ends up with the expression "\\b.\\b", which will only ever match
> a single character with word break on either side (so, in your
> example, it should match all and only the spaces):
>
> > "Hello World and Google"
>        ^     ^   ^
>
> Closer would be "\\b.+?\\b", but that would still match on your spaces:
>
> > "Hello World and Google"
>   ^    ^^    ^^  ^^
>
> If you really want words, you are best off deciding what constitutes a
> word, and then writing the regex for exactly that purpose.  There is
> the built-in "\\w" character class, but only you can decide whether
> things like apostrophes and hyphens break words.  (And that's just in
> English; I have no idea what constitutes word-break most other
> languages!)  For English, I'd consider something like "[\\w'-]+"
> (which should be: all word chars, plus apostrophes, plus hyphens).
>
> And from a personal taste point of view, I'd likely write it exactly
> that way.  (I do sometimes decompose my regexes, but only if they have
> repeated subsections that could better be described as a variable
> name.)
>
> You also had a small logic error, when you wrote this:
>
>           OffSetMap[foundPos] = foundLen;
>
> "foundPos" is relative to the start of the last search, not to the
> start of the whole string.
>
> Here's my version:
>
> | #include <map>
> | #include <string>
> |
> | #include <boost/foreach.hpp>
> | #include <boost/regex.hpp>
> |
> | typedef int int32;
> |
> | typedef std::map< int32, int32 > offset_map_t;
> |
> | void create_offset_map( const std::string & str,
> |                         offset_map_t & offset_map )
> | {
> |     std::cout << "searching '" << str << "'" << std::endl;
> |
> |     boost::regex re( "[\\w'-]+" );
> |
> |     boost::smatch what;
> |
> |     std::string::const_iterator start = str.begin();
> |     std::string::const_iterator end   = str.end();
> |
> |     while ( boost::regex_search( start, end, what, re ) )
> |     {
> |         int32 pos = what.position();
> |         int32 len = what.length();
> |
> |         std::cout << "  found '" << what.str( 0 ) << "'"
> |                   << " at pos=" << pos << ", len=" << len << std::endl;
> |
> |         start += pos;
> |         offset_map[ start - str.begin() ] = len;
> |         start += len;
> |     }
> |
> |     BOOST_FOREACH( const offset_map_t::value_type & p, offset_map )
> |         std::cout << "    ( " << p.first << ", "
> |                   << p.second << " )" << std::endl;
> | }
> |
> | int main( int argc, char * argv [] )
> | {
> |     for ( int i = 1; i < argc; ++i )
> |     {
> |         offset_map_t my_map;
> |         create_offset_map( argv[i], my_map );
> |     }
> |     return 0;
> | }
>
> Hope this helps.
>
> Best Regards,
> Anthony Foiani
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