[Bug libstdc++/84110] Null character in regex

[abigail.buccaneer at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84110

--- Comment #1 from AbigailBuccaneer <abigail.buccaneer at gmail dot com> ---
From what I can tell, this isn't intentional behavior in libstdc++.

regex_scanner.h defines:

    const char* _M_ecma_spec_char = "^$\\.*+?()[]{}|";

and regex_scanner.tcc tries to interpret any character not in this set of
special characters as an ordinary character token:

      if (std::strchr(_M_spec_char, _M_ctype.narrow(__c, ' ')) == nullptr)
        {
          _M_token = _S_token_ord_char;
          _M_value.assign(1, __c);
          return;
        }

However, the strchr specification says (emphasis mine):

Description: The strchr function locates the first occurrence of c (converted 
to a char) in the string pointed to by s. ***The terminating null character is
considered to be part of the string***.