C++11 Time – How to Print Current Time with Milliseconds Using C++

c++c++11linuxtimewindows

Currently I use this code

string now() {
    time_t t = time(0);
    char buffer[9] = {0};

    strftime(buffer, 9, "%H:%M:%S", localtime(&t));
    return string(buffer);
}

to format time. I need to add milliseconds, so the output has the format: 16:56:12.321

Best Answer

Don't waste your time with Boost (I know many will be offended by this statement and consider it heresy).

This discussion contains two very workable solutions that don't require you to enslave yourself to non-standard, 3rd party libraries.

C++ obtaining milliseconds time on Linux -- clock() doesn't seem to work properly

http://linux.die.net/man/3/clock_gettime

References to gettimeofday can be found here at opengroup.org

Related Solutions

C++ – How to Print Current System Time with Milliseconds in C++11

Using code from this answer:

#include <chrono>
#include <ctime>
#include <iostream>

template <typename Duration>
void print_time(tm t, Duration fraction) {
    using namespace std::chrono;
    std::printf("[%04u-%02u-%02u %02u:%02u:%02u.%03u]\n", t.tm_year + 1900,
                t.tm_mon + 1, t.tm_mday, t.tm_hour, t.tm_min, t.tm_sec,
                static_cast<unsigned>(fraction / milliseconds(1)));

    // VS2013's library has a bug which may require you to replace
    // "fraction / milliseconds(1)" with
    // "duration_cast<milliseconds>(fraction).count()"
}

int main() {
    using namespace std;
    using namespace std::chrono;

    system_clock::time_point now = system_clock::now();
    system_clock::duration tp = now.time_since_epoch();

    tp -= duration_cast<seconds>(tp);

    time_t tt = system_clock::to_time_t(now);

    print_time(*gmtime(&tt), tp);
    print_time(*localtime(&tt), tp);
}

One thing to keep in mind is that the fact that the timer returns values of sub-millisecond denominations does not necessarily indicate that the timer has sub-millisecond resolution. I think Windows' implementation in VS2015 may finally be fixed, but the timer they've been using to back their chrono implementation so far has been sensitive to the OS timeBeginPeriod() setting, displaying varying resolution, and the default setting is I think 16 milliseconds.

Also the above code assumes that neither UTC nor your local timezone are offset from the epoch of std::chrono::system_clock by a fractional second value.

Example of using Howard's date functions to avoid ctime: http://coliru.stacked-crooked.com/a/98db840b238d3ce7

C++ Chrono – Print Current System Time in Nanoseconds

[EDIT]

Changing the code to C++ style:

#include <chrono>
#include <ctime>

std::chrono::time_point<std::chrono::system_clock> now = std::chrono::system_clock::now();
auto duration = now.time_since_epoch();

typedef std::chrono::duration<int, std::ratio_multiply<std::chrono::hours::period, std::ratio<8>
>::type> Days; /* UTC: +8:00 */

Days days = std::chrono::duration_cast<Days>(duration);
    duration -= days;
auto hours = std::chrono::duration_cast<std::chrono::hours>(duration);
    duration -= hours;
auto minutes = std::chrono::duration_cast<std::chrono::minutes>(duration);
    duration -= minutes;
auto seconds = std::chrono::duration_cast<std::chrono::seconds>(duration);
    duration -= seconds;
auto milliseconds = std::chrono::duration_cast<std::chrono::milliseconds>(duration);
    duration -= milliseconds;
auto microseconds = std::chrono::duration_cast<std::chrono::microseconds>(duration);
    duration -= microseconds;
auto nanoseconds = std::chrono::duration_cast<std::chrono::nanoseconds>(duration);

std::cout << hours.count() << ":"
          << minutes.count() << ":"
          << seconds.count() << ":"
          << milliseconds.count() << ":"
          << microseconds.count() << ":"
          << nanoseconds.count() << std::endl;

Result:

17:56:14:94:451:679

[Old]

A simply example:

#include <sys/time.h>

char fmt[64];
char buf[64];
struct timeval tv;
struct tm *tm;

gettimeofday (&tv, NULL);
tm = localtime (&tv.tv_sec);
strftime (fmt, sizeof (fmt), "%H:%M:%S:%%06u", tm);
snprintf (buf, sizeof (buf), fmt, tv.tv_usec);
printf ("%s\n", buf);

Result:

00:01:32:695240

Best Answer

Related Solutions

C++ – How to Print Current System Time with Milliseconds in C++11

C++ Chrono – Print Current System Time in Nanoseconds

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