[:xdigit:] does not work with std::wstring in a Cygwin environment

[Corinna Vinschen]

On Feb 11 16:02, Gans, Markus wrote:
> This seems to be an internal Cygwin error:
> 
> https://www.reddit.com/r/cpp_questions/comments/sp52gq/xdigit_does_not_work_with_stdwstring_in_a_cygwin/
> 
> ------------------------------------------------------------------------------
> I have an unexpected behavior with Cygwin for the character class [:xdigit:]. The pattern matching for [:xdigit:] behaves like the pattern matching of [:digit:] when using a wide string. With `std::string` everything works fine.
> 
> Example:
> 
>     #include <iostream>
>     #include <string>
>     #include <regex>
>     
>     int main ()
>     {
>       std::cout << "Wide character string\n";
>       std::wstring w_character = L"a";
>     
>       if ( regex_match(w_character, std::wregex(L"[[:xdigit:]]")) )
>         std::cout << "'" << char(w_character[0]) << "' is a hex digit\n";
>       else
>         std::cout << "'" << char(w_character[0]) << "' is not a hex digit\n";
>     
>       std::cout << "----------------------\n"
>                 << "String with 1 byte character\n";
>       std::string character = "a";
>     
>       if ( regex_match(character, std::regex("[[:xdigit:]]")) )
>         std::cout << "'" << char(w_character[0]) << "' is a hex digit\n";
>       else
>         std::cout << "'" << char(w_character[0]) << "' is not a hex digit\n";
>     
>       return 0;
>     }
> 
> Output in a Cygwin environment:
> 
>     Wide character string
>     'a' is not a hex digit
>     ----------------------
>     Character string
>     'a' is a hex digit
> 
> Output on Linux:
> 
>     Wide character string
>     'a' is a hex digit
>     ----------------------
>     String with 1 byte character
>     'a' is a hex digit
> 
> Question: Why does Cygwin not detect the letters a, b, c, d, e, and f as hexadecimal digits in a wide string?
> ------------------------------------------------------------------------------

This seems to be a bug in libstdc++.  None of the above functions call
any internal library function which could affect the result.  That means
regcomp(3), regexec(3), isxdigit{_l}(3) or iswxdigit{_l}(3).

Achim, any idea?  Is wchar support broken in Cygwin's libstdc++, by any
chance?


Corinna