[Boost-users] regex expressions in boost::regex vs python, how to get the answer from boost

From: Alexis H. Rivera-Rios (ahrivera_at_[hidden])
Date: 2005-03-28 16:34:37

Hi,

I'm playing around with the boost::regex library and I
want to match two tokens from a filename.  For example
files with the following format:

myname_123.dat

I want to be able to determine the string and number
separated by the underscore.  So the result of my
match should be "myname", and 123.

In python, I can do it like this:
import re
>>> x = 'myclass_123.dat'
>>> result = re.match(r'(\w+)_(\d+)\.dat$', x)
>>> result.group(1)
'myclass'
>>> result.group(2)
'123'

I'm having problems getting the same result in C++. 
This is the sample program:

int main(int argc, const char** argv)
{
   boost::regex expression("(\\w+)_(\\d+)\\.dat$");   
    
   std::string filename(argv[1]);

   boost::cmatch what; 
                  
    if(boost::regex_search(filename.c_str(), what,
expression)) 
    {
        for (int i=0;i<what.size();++i)
        {
           std::cout << what[i].first << " " 
                     << what[i].second << std::endl;	
        }
   }
   return 0;
}

The output of this program is:
> openmp3 alexis_1023.dat
alexis_1023.dat
alexis_1023.dat _1023.dat
1023.dat .dat

How do I get my groups "alexis", 123 as in Python?

Thanks,
Alexis

Programming Tutorial:
In Python: To do this, do this
In Perl: To do this, do this or this or this or this...
In C: To do this, do this, but be careful
In C++: To do this, do this, but don't do this, be careful of this, watch out for this, and whatever you do, don't do this

                
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