Formatting ptime does not produce time zone information in the output

[Lastique]

When the time type is boost::posix_time::ptime, Boost.DateTime output facets don't produce any output for "%Z", "%z", "%Q" and "%q" flags.

Here is an example:

#include <ctime>
#include <iostream>
#include <locale>
#include <boost/date_time.hpp>

static const char format[] = "%Y-%m-%d %H:%M:%S %z";

int main()
{
    auto *facet = new boost::posix_time::time_facet(format);
    std::locale loc(std::locale(), facet);
    std::locale::global(loc);
    std::cout.imbue(loc);

    auto now = boost::posix_time::microsec_clock::local_time();

    std::cout << '"' << now << '"' << std::endl;

    std::time_t time_t_now = boost::posix_time::to_time_t(now);
    std::tm tm_buf = {};
    std::tm* tm_now = boost::date_time::c_time::localtime(&time_t_now, &tm_buf);

    char buf[128];
    std::strftime(buf, sizeof(buf), format, tm_now);
    std::cout << '"' << buf << '"' << std::endl;
}

Output:

"2023-07-02 17:36:16"
"2023-07-02 20:36:16 +0300"

I would expect the time zone format flags to work and result in the current system time zone in the output.