Put first boost::regex match into a string

Question

Somehow, I've failed to find out, how to put only the first occurrence or regular expression to string. I can create a regex object:

static const boost::regex e("<(From )?([A-Za-z0-9_]+)>(.*?)");

Now, I need to match ([A-Za-z0-9_]+) to std::string, say playername.

std::string chat_input("<Darker> Hello");
std::string playername = e.some_match_method(chat_input, 1);   //Get contents of the second (...)

What have I missed?
What should be instead of some_match_method and what parameters should it take?

Its not my problem to match the occurrence, but to get the match results. So the string does not matter. I'll include it anyway. — Tomáš Zato, Mar 21 '13 at 21:03
Sure, but if you change the regex to `(?<=<(From )?)([A-Za-z0-9_]+)(?=>(.*?))` you don't have to care about that. — eandersson, Mar 21 '13 at 21:07

score 6 · Answer 1 · edited May 08 '18 at 14:19

You can do something like this:

static const regex e("<(From )?([A-Za-z0-9_]+)>(.*?)");
string chat_input("<Darker> Hello");
smatch mr;
if (regex_search(begin(chat_input), end(chat_input), mr, e)
    string playername = mr[2].str();   //Get contents of the second (...)

Please note that regex is part of C++11, so you don't need boost for it, unless your regular expression is complex (as C++11 and newer still has difficulties processing complex regular expressions).

score 4 · Accepted Answer · answered Mar 21 '13 at 21:11

I think what you're missing is that boost::regex is the regular expression, but it doesn't do the parsing against a given input. You need to actually use it as a parameter to boost::regex_search or boost::regex_match, which evaluate a string (or iterator pairs) against the regular expression.

static const boost::regex e("<(From )?([A-Za-z0-9_]+)>(.*?)"); 
std::string chat_input("<Darker> Hello");
boost::match_results<std::string::const_iterator> results;
if (boost::regex_match(chat_input, results, e))
{
     std::string playername = results[2];  //Get contents of the second (...)
}

Put first boost::regex match into a string

2 Answers2