Convert std::duration to human readable time

Agreed there is no standard implementation. Here is how you can write one yourself:

#include <iostream>
#include <iomanip>
#include <chrono>

std::ostream&
display(std::ostream& os, std::chrono::nanoseconds ns)
{
    using namespace std;
    using namespace std::chrono;
    typedef duration<int, ratio<86400>> days;
    char fill = os.fill();
    os.fill('0');
    auto d = duration_cast<days>(ns);
    ns -= d;
    auto h = duration_cast<hours>(ns);
    ns -= h;
    auto m = duration_cast<minutes>(ns);
    ns -= m;
    auto s = duration_cast<seconds>(ns);
    os << setw(2) << d.count() << "d:"
       << setw(2) << h.count() << "h:"
       << setw(2) << m.count() << "m:"
       << setw(2) << s.count() << 's';
    os.fill(fill);
    return os;
};

int
main()
{
    std::cout << "Operation took ";
    display(std::cout, std::chrono::microseconds(918734000000));
    std::cout << '\n';
}

Operation took 10d:15h:12m:14s

Based on Howard's answer, I wrote this to make sure that only the relevant data is printed out, so 120 seconds becomes 2m00s instead of 00d:00h:02m00s, and made sure to strip the leading zero, so its still 2m00s and not 02m00s.

Usage is simple:

std::chrono::seconds seconds{60*60*24 + 61};

std::string pretty_seconds = beautify_duration(seconds);
printf("seconds: %s", pretty_seconds.c_str());
>>seconds: 1d00h01m01s

Code:

std::string beautify_duration(std::chrono::seconds input_seconds)
{
    using namespace std::chrono;
    typedef duration<int, std::ratio<86400>> days;
    auto d = duration_cast<days>(input_seconds);
    input_seconds -= d;
    auto h = duration_cast<hours>(input_seconds);
    input_seconds -= h;
    auto m = duration_cast<minutes>(input_seconds);
    input_seconds -= m;
    auto s = duration_cast<seconds>(input_seconds);

    auto dc = d.count();
    auto hc = h.count();
    auto mc = m.count();
    auto sc = s.count();

    std::stringstream ss;
    ss.fill('0');
    if (dc) {
        ss << d.count() << "d";
    }
    if (dc || hc) {
        if (dc) { ss << std::setw(2); } //pad if second set of numbers
        ss << h.count() << "h";
    }
    if (dc || hc || mc) {
        if (dc || hc) { ss << std::setw(2); }
        ss << m.count() << "m";
    }
    if (dc || hc || mc || sc) {
        if (dc || hc || mc) { ss << std::setw(2); }
        ss << s.count() << 's';
    }

    return ss.str();
}

Here is a version that allows you to inline a duration with operator<< It only prints what is necessary and allows setting the precision you want:

#include <chrono>
#include <iomanip>
#include <optional>
#include <ostream>

std::ostream& operator<<(std::ostream& os, std::chrono::nanoseconds ns)
{
    using namespace std::chrono;
    using days = duration<int, std::ratio<86400>>;
    auto d = duration_cast<days>(ns);
    ns -= d;
    auto h = duration_cast<hours>(ns);
    ns -= h;
    auto m = duration_cast<minutes>(ns);
    ns -= m;
    auto s = duration_cast<seconds>(ns);
    ns -= s;

    std::optional<int> fs_count;
    switch (os.precision()) {
    case 9: fs_count = ns.count();
        break;
    case 6: fs_count = duration_cast<microseconds>(ns).count();
        break;
    case 3: fs_count = duration_cast<milliseconds>(ns).count();
        break;
    }

    char fill = os.fill('0');
    if (d.count())
        os << d.count() << "d ";
    if (d.count() || h.count())
        os << std::setw(2) << h.count() << ":";
    if (d.count() || h.count() || m.count())
        os << std::setw(d.count() || h.count() ? 2 : 1) << m.count() << ":";
    os << std::setw(d.count() || h.count() || m.count() ? 2 : 1) << s.count();
    if (fs_count.has_value())
        os << "." << std::setw(os.precision()) << fs_count.value();
    if (!d.count() && !h.count() && !m.count())
        os << "s";

    os.fill(fill);
    return os;
}

Here are some usage examples:

#include <iostream>
#include <chrono>

using namespace std;
using namespace std::chrono_literals;
int main()
{
    cout << 918734032564785ns << "\n";
    cout << setprecision(3) << 918734032564785ns << "\n";
    cout << setprecision(9) << 918734032564785ns << "\n";
    cout << setprecision(0) << 918734032564785ns << "\n";
    cout << setprecision(3) << 432034ms << "\n";
    cout << 14h + 32min + 37s + 645ms << "\n";
    cout << 86472s << "\n";
    cout << 4324ms << "\n";

    return 0;
}

Output:

10d 15:12:14.032564
10d 15:12:14.032
10d 15:12:14.032564785
10d 15:12:14
7:12.034
14:32:37.645
1d 00:01:12.000
4.324s