Re: [Boost-users] Regular expression problem using literals

Subject: Re: [Boost-users] Regular expression problem using literals
From: Eric Niebler (eric_at_[hidden])
Date: 2012-12-11 13:17:27

On 12/11/2012 10:03 AM, Neil Sutton wrote:
> Hello, I am learning the basics of regular expression syntax and have
> been looking at the following example:
> #include <iostream>
> #include <fstream>
> #include <string>
> #include <boost/regex.hpp>
> #include <boost/xpressive/xpressive.hpp>
> 
> using namespace boost::xpressive;
> 
> int main()
> {
>   std::ifstream input("myfile");
>   if(input)
>     std::cout << "Success\n";
>   else
>     std::cout << "fail\n";
> 
>   std::string line;
>   std::string data;
>   
> while (getline(input, line))
> {
>    data += line; 
> } 
> 
> std::string const &ref = data;
> mark_tag day(1), month(2), year(3), delim(4);
> sregex date = (month= repeat<1,2>(_d))  // find the month ...
>                >> (delim= (set= '/','-'))            // followed by a
> delimiter ...
>                >> (day=   repeat<1,2>(_d)) >> delim  // and a day
> followed by the same 
>                >> (year=  repeat<1,2>(_d >> _d));    // and the year.
> smatch what;
> 
>     if( regex_search(ref, what, date ) )
>     {
>         std::cout << what[0]     << '\n'; // whole match
>         std::cout << what[day]   << '\n'; // the day
>         std::cout << what[month] << '\n'; // the month
>         std::cout << what[year]  << '\n'; // the year
>         std::cout << what[delim] << '\n'; // the delimiter
>     }
> return 0;
> }
> 
> My problem is very simple and I am sorry to be asking about it. I want
> to include some literal wording in my regular expression. For example,
> before the program outputs the date it also searches for the words
> "Football results for" - (then date is output). Please can you show me
> how to prefix this regular expression with the literal words? My
> compiler see the 'for' as a c++ keyword, without more.

How about:

sregex date = "Football results for "
           >> (month= repeat<1,2>(_d))
           >> (delim= (set= '/','-'))
           >> (day=   repeat<1,2>(_d)) >> delim
           >> (year=  repeat<1,2>(_d >> _d));

?

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