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?
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