C++ date library fails with timezone - c++

Question

This used to play once. I am trying to get some data from the C++ date library but an exception is caught. I am compiling with
-DUSE_AUTOLOAD=0 -DHAS_REMOTE_API=0 -DUSE_OS_TZDB=1
what is wrong with the code?
#include <iostream>
#include "date/tz.h"
#include <exception>
using namespace date;
using namespace std::chrono;
int main(int argc, char** argv) {
try {
auto current_time_zone = make_zoned("Europe/Athens", std::chrono::system_clock::now());
auto current_day = date::format("%A", current_time_zone);
auto current_time = date::format("%H:%M", current_time_zone);
std::cout << "day: " << current_day << ", time: " << current_time << " in timezone: " << current_time_zone << std::endl;
//std::cout << " in timezone: " << current_time_zone << std::endl;
} catch ( std::exception& e) {
std::cout << e.what() << std::endl;
}
}

Answer 1

You need to use the -pthread flag. tz.cpp uses call_once to do part of the initialisation. And without -pthread it's not going to work (as underneath it need something like __gthread_once). See this for more details.
You can verify if that's the problem by running your example with gdb (use the catch throw).

Answer 2

I'm not positive what the problem is, but I can tell you that this library does not throw an exception that contains the message "Unknown error".
Try adding -DONLY_C_LOCALE=1 to your build flags. This will avoid your std::lib's time_put facet, but will limit you to only the "C" locale. If this fixes the problem, then it is your std::lib's std::time_put facet that threw the exception.