`std::put_time` with "%X" doesn't seem to take locale into account on macOS

Runtimes C++
1

I realized that when imbuing a stringstream with a locale and then calling std::put_time with the format %X, which is a locale-dependent time, the time doesn’t change to be dependent on macOS. This does seem to work on Windows, however. I’ll attach a basic C++ file showing off this quirk, and I’ll put the outputs that I see below:

# macOS
Current time (US): 15:52:27
Current time (UK): 15:52:27

# Windows
Current time (US): 4:05:28 PM
Current time (UK): 16:05:28

Here’s a basic example:

#include <string>
#include <sstream>
#include <iomanip>
#include <iostream>
#include <chrono>

std::string TimeAsString(const std::chrono::system_clock::time_point& tp, const std::string& strLocale = "")
{
    const std::time_t tt = std::chrono::system_clock::to_time_t(tp);
    if (tt > 0)
    {
        std::tm ti;
#if defined(_WIN32)
        localtime_s(&ti, &tt);
#else
        localtime_r(&tt, &ti);
#endif
        const auto locale = std::locale(strLocale);
        std::stringstream ss;
        ss.imbue(locale);
        ss << std::put_time(&ti, "%X");
        return ss.str();
    }
    return "N/A";
}

int main()
{
    const auto now = std::chrono::system_clock::now();
    std::cout << "Current time (US): " << TimeAsString(now, "en_US") << std::endl;
    std::cout << "Current time (UK): " << TimeAsString(now, "en_GB") << std::endl;
    return 0;
}

Does anyone have any idea why this is happening?