extract a string with single quotes between parenthesis and single quote

Question

I have the following code :

  #include 
#include 

using namespace std;

int main()
{
  string s;

      s = \"server (\'m1.labs         


        

Answer 1

You should look at look-around and conditional regexp.
And regex engine should be PCRE compatible. (I don't know about C++)

You should newer use regexp, you have found in the internet if you dont understand it.

Try something like '((?:[^']|'')*?)'(?!') (demo on 101regex)

Answer 2

But how can I make the regex so that it is able to extract escaped single quotes (example username (user''5) should be extracted as 'user'5'.

Ugh. Is that what you meant? I was right about X/Y problem then.

Note: What you describe is known as escaping special characters. Two common ways to escape special characters:

1. repeat it (e.g. printf("100%%"); to print 100%)

2. introduce it using another escape (usually backslash). E.g.

   std::cout << "Hello \"World\"" << std::endl;
   

   Or, one more intricate example:

   std::cout << "Newline is \\n" << std::endl;
   

Here you go: just add q >> char_(q) to accept repeated quotes as quote-escape:

auto quoted = [](char q) { 
    return lexeme[ q >> *(
              q >> char_(q)  // accept repeated quotes as quote-escape
            | '\\' >> char_  // accept backs-slash escape
            | char_ - q      // accept any other non-quote
         ) >> q]; };

Nothing else changes relative to tokenizing string , accepting everything between given set of characters in CPP

Live On Coliru

#include <iostream>
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/adapted/std_pair.hpp>
#include <map>

using Config = std::map<std::string, std::string>;
using Entry  = std::pair<std::string, std::string>;

namespace parser {
    using namespace boost::spirit::x3;

    template <typename T> auto as = [](auto p) { return rule<struct _, T> {} = p; };
    auto quoted = [](char q) { return lexeme[q >> *(q >> char_(q) | '\\' >> char_ | char_ - q) >> q]; };

    auto value  = quoted('\'') | quoted('"');
    auto key    = lexeme[+alpha];
    auto pair   = key >> '(' >> value >> ')';
    auto config = skip(space) [ *as<Entry>(pair) ];
}

Config parse_config(std::string const& cfg) {
    Config parsed;
    auto f = cfg.begin(), l = cfg.end();
    if (!parse(f, l, parser::config, parsed))
        throw std::invalid_argument("Parse failed at " + std::string(f,l));
    return parsed;
}

int main() {
    auto const text = "server ('m1.labs.teradata.com') username ('use'')r_*5') password('u\" er 5') dbname ('default')";
    Config cfg = parse_config(text);

    for (auto& setting : cfg)
        std::cout << "Key " << setting.first << " has value " << setting.second << "\n";
}

Prints

Key dbname has value default
Key password has value u" er 5
Key server has value m1.labs.teradata.com
Key username has value use')r_*5