Using regular expressions with C++ on Unix

Question

I'm familiar with Regex itself, but whenever I try to find any examples or documentation to use regex with Unix computers, I just get tutorials on how to write regex or how to use the .NET specific libraries available for Windows. I've been searching for a while and I can't find any good tutorials on C++ regex on Unix machines.

What I'm trying to do:

Parse a string using regex by breaking it up and then reading the different subgroups. To make a PHP analogy, something like preg_match that returns all $matches.

Answer 1

Consider using Boost.Regex.

An example (from the website):

bool validate_card_format(const std::string& s)
{
   static const boost::regex e("(\\d{4}[- ]){3}\\d{4}");
   return regex_match(s, e);
}

Another example:

// match any format with the regular expression:
const boost::regex e("\\A(\\d{3,4})[- ]?(\\d{4})[- ]?(\\d{4})[- ]?(\\d{4})\\z");
const std::string machine_format("\\1\\2\\3\\4");
const std::string human_format("\\1-\\2-\\3-\\4");

std::string machine_readable_card_number(const std::string s)
{
   return regex_replace(s, e, machine_format, boost::match_default | boost::format_sed);
}

std::string human_readable_card_number(const std::string s)
{
   return regex_replace(s, e, human_format, boost::match_default | boost::format_sed);
}

Answer 2

Look up the documentation for TR1 regexes or (almost equivalently) boost regex. Both work quite nicely on various Unix systems. The TR1 regex classes have been accepted into C++ 0x, so though they're not exactly part of the standard yet, they will be reasonably soon.

Edit: To break a string into subgroups, you can use an sregex_token_iterator. You can specify either what you want matched as tokens, or what you want matched as separators. Here's a quickie demo of both:

#include <iterator>
#include <regex>
#include <string>
#include <iostream>

int main() { 

    std::string line;

    std::cout << "Please enter some words: " << std::flush;
    std::getline(std::cin, line);

    std::tr1::regex r("[ .,:;\\t\\n]+");
    std::tr1::regex w("[A-Za-z]+");

    std::cout << "Matching words:\n";
    std::copy(std::tr1::sregex_token_iterator(line.begin(), line.end(), w),
        std::tr1::sregex_token_iterator(), 
        std::ostream_iterator<std::string>(std::cout, "\n"));

    std::cout << "\nMatching separators:\n";
    std::copy(std::tr1::sregex_token_iterator(line.begin(), line.end(), r, -1), 
        std::tr1::sregex_token_iterator(), 
        std::ostream_iterator<std::string>(std::cout, "\n"));

    return 0;
}

If you give it input like this: "This is some 999 text", the result is like this:

Matching words:
This
is
some
text

Matching separators:
This
is
some
999
text