[Bug libstdc++/82513] New: regex [z\-a] fails to compile

[gene at genethomas dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82513

            Bug ID: 82513
           Summary: regex [z\-a] fails to compile
           Product: gcc
           Version: 5.4.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: gene at genethomas dot com
  Target Milestone: ---

The regex [z\-a] fails to compile in <regex> and throws a regex_error. It seems
to be interpreting the \- as a - and thinking the z-a range is invalid. Sample
program below:

#include <regex>
#include <iostream>
#include <exception>

using namespace std;

int main(int argc, char **argv) {

    try {
        regex::flag_type flags = regex::ECMAScript;
        regex theRegex("[z\\-a]", flags);
        cout << "ok\n";
        return 0;
    } catch (exception &e) {
        cerr << "fatal error: " << e.what() << "\n";
        return 1;
    }
}