id,summary,reporter,owner,description,type,status,milestone,component,version,severity,resolution,keywords,cc
13256,regex '([|&])\1?' with backreference fails to compile if regex::nosub flag used,Gene Thomas <gene@…>,John Maddock,"when compiling a regex with regex::nosubs flag set, a regex with a back reference fails with: 

Invalid back reference: specified capturing group does not exist.  The error occurred while parsing the regular expression: '([|&])>>>HERE>>>\1?'.

Test program:

#include <boost/regex.hpp>
#include <iostream>
#include <exception>

using namespace std;

int main(int argc, char **argv) {
    
    try {
        boost::regex::flag_type flags = boost::regex::ECMAScript;
        flags |= boost::regex::nosubs;
        boost::regex theRegex(""([|&])\\1?"", flags);
        cout << ""ok\n"";
        return 0;
    } catch (exception &e) {
        cerr << ""exception: "" << e.what() << ""\n"";
        return 1;
    }
}
    
g++ -std=c++11 test-boost-regex-bug.cpp -o test-boost-regex-bug -l boost_regex",Bugs,new,To Be Determined,regex,Boost 1.58.0,Problem,,regex nosub,gcc