I have been upgrading some old code and have been trying to update to c++11 where possible. The following code is how I used to display the time and date in my program
#include <iostream>
#include <string>
#include <stdio.h>
#include <time.h>
const std::string return_current_time_and_date() const
{
time_t now = time(0);
struct tm tstruct;
char buf[80];
tstruct = *localtime(&now);
strftime(buf, sizeof(buf), "%Y-%m-%d %X", &tstruct);
return buf;
}
I would like to output the current time and date in a similar format using std::chrono(or similar) but am unsure how to go about doing so. Any help would be greatly appreciated. Thanks
The <chrono>
library only deals with time and not dates, except for the system_clock
which has the ability to convert its timepoints to time_t
. So using <chrono>
for dates will not improve things much. Hopefully we get something like chrono::date
in the not too distant future.
That said, you can use <chrono>
in the following way:
#include <chrono> // chrono::system_clock
#include <ctime> // localtime
#include <sstream> // stringstream
#include <iomanip> // put_time
#include <string> // string
std::string return_current_time_and_date()
{
auto now = std::chrono::system_clock::now();
auto in_time_t = std::chrono::system_clock::to_time_t(now);
std::stringstream ss;
ss << std::put_time(std::localtime(&in_time_t), "%Y-%m-%d %X");
return ss.str();
}
Note that std::localtime
may cause data races. localtime_r
or similar functions may be available on your platforms.
Update:
Using a new version of Howard Hinnant's date library you can write:
#include "date.h"
#include <chrono>
#include <string>
#include <sstream>
std::string return_current_time_and_date() {
auto now = std::chrono::system_clock::now();
auto today = date::floor<days>(now);
std::stringstream ss;
ss << today << ' ' << date::make_time(now - today) << " UTC";
return ss.str();
}
This will print out something like "2015-07-24 05:15:34.043473124 UTC".
On an unrelated note, returning const
objects has become undesirable with C++11; const return values cannot be moved from. I also removed the trailing const because trailing const is only valid for member functions and this function has no need to be a member.