time since epoch to string using boost

Question

auto timeSinceEpoch = boost::chrono::duration_cast<boost::chrono::microseconds>(boost::chrono::steady_clock::now().time_since_epoch()).count();

boost::posix_time::ptime now(boost::gregorian::date(1970, 1, 1), boost::posix_time::microsec(static_cast<std::int64_t>(timeSinceEpoch)));

std::string str = boost::posix_time::to_iso_string(now);

Output : 19700114T232422.133653 which it is incorrect, what am I doing wrong ?

Answer 1

On some systems, the epoch of steady_clock is nanoseconds since boot.

You will get a more useful expected result with other clocks:

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#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/chrono.hpp>
#include <string>
#include <iostream>

int main()
{
    boost::posix_time::ptime const time_epoch(boost::gregorian::date(1970, 1, 1));

    auto ms = (boost::posix_time::microsec_clock::local_time() - time_epoch).total_microseconds();
    std::cout << "microseconds: " << ms << "\n";

    boost::posix_time::ptime now = time_epoch + boost::posix_time::microseconds(ms);
    std::cout << boost::posix_time::to_iso_string(now);
}

Prints

microseconds: 1415115992000000
20141104T154632