C++ timestamp with milliseconds (chrono + fmtlib)

timestamp_with_ms.cpp

// https://godbolt.org/z/7WW5vTsaY

#include <chrono>
#include <fmt/format.h>
#include <fmt/chrono.h>

int main()
{
    const auto now = std::chrono::system_clock::now();
    const auto now_sec = std::chrono::time_point_cast<std::chrono::seconds>(now);
    const auto now_ms = std::chrono::time_point_cast<std::chrono::milliseconds>(now);
    const auto ms = now_ms.time_since_epoch().count() % std::milli::den;
    const auto ts = fmt::format("{:%FT%T}.{:03d}Z", now_sec, ms);
    fmt::print("{}\n", ts);
}

// Sample output:
// 2024-10-30T07:50:08.553Z