How to print current time (with milliseconds) using C++ / C++11

Question

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

Answer 1

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

Answer 2

You can use Boost's Posix Time.

You can use boost::posix_time::microsec_clock::local_time() to get current time from microseconds-resolution clock:

boost::posix_time::ptime now = boost::posix_time::microsec_clock::local_time(); 

Then you can compute time offset in current day (since your duration output is in the form <hours>:<minutes>:<seconds>.<milliseconds>, I'm assuming they are calculated as current day offset; if they are not, feel free to use another starting point for duration/time interval):

boost::posix_time::time_duration td = now.time_of_day(); 

Then you can use .hours(), .minutes(), .seconds() accessors to get the corresponding values.
Unfortunately, there doesn't seem to be a .milliseconds() accessor, but there is a .total_milliseconds() one; so you can do a little subtraction math to get the remaining milliseconds to be formatted in the string.

Then you can use sprintf() (or sprintf()_s if you are interested in non-portable VC++-only code) to format those fields into a raw char buffer, and safely wrap this raw C string buffer into a robust convenient std::string instance.

See the commented code below for further details.

Output in console is something like:

11:43:52.276

---

Sample code:

///////////////////////////////////////////////////////////////////////////////  #include <stdio.h>      // for sprintf()  #include <iostream>     // for console output #include <string>       // for std::string  #include <boost/date_time/posix_time/posix_time.hpp>   //----------------------------------------------------------------------------- // Format current time (calculated as an offset in current day) in this form: // //     "hh:mm:ss.SSS" (where "SSS" are milliseconds) //----------------------------------------------------------------------------- std::string now_str() {     // Get current time from the clock, using microseconds resolution     const boost::posix_time::ptime now =          boost::posix_time::microsec_clock::local_time();      // Get the time offset in current day     const boost::posix_time::time_duration td = now.time_of_day();      //     // Extract hours, minutes, seconds and milliseconds.     //     // Since there is no direct accessor ".milliseconds()",     // milliseconds are computed _by difference_ between total milliseconds     // (for which there is an accessor), and the hours/minutes/seconds     // values previously fetched.     //     const long hours        = td.hours();     const long minutes      = td.minutes();     const long seconds      = td.seconds();     const long milliseconds = td.total_milliseconds() -                               ((hours * 3600 + minutes * 60 + seconds) * 1000);      //     // Format like this:     //     //      hh:mm:ss.SSS     //     // e.g. 02:15:40:321     //     //      ^          ^     //      |          |     //      123456789*12     //      ---------10-     --> 12 chars + \0 --> 13 chars should suffice     //       //      char buf[40];     sprintf(buf, "%02ld:%02ld:%02ld.%03ld",          hours, minutes, seconds, milliseconds);      return buf; }  int main() {     std::cout << now_str() << '\n';     }  /////////////////////////////////////////////////////////////////////////////// 

Answer 3

Here is a solution I found without using boost

std::string getCurrentTimestamp()
{
using std::chrono::system_clock;
auto currentTime = std::chrono::system_clock::now();
char buffer[80];

auto transformed = currentTime.time_since_epoch().count() / 1000000;

auto millis = transformed % 1000;

std::time_t tt;
tt = system_clock::to_time_t ( currentTime );
auto timeinfo = localtime (&tt);
strftime (buffer,80,"%F %H:%M:%S",timeinfo);
sprintf(buffer, "%s:%03d",buffer,(int)millis);

return std::string(buffer);
}