C++11 get current date and time as string

Question

What is the state of the art way to get date and time as string in c++11?

I know about std::put_time, but the reference says I shall use it only in streams.

There is std::chrono::system_clock which provides to_time_t returning the time as time_t and lacking the date, doesn't it?

I could use a stringstream like bames53: Outputting Date and Time in C++ using std::chrono but that seems to be a workaround.

Answer 1

Using Howard Hinnant's free, open-source header-only datetime library, you can get the current UTC time as a std::string in a single line of code:

std::string s = date::format("%F %T", std::chrono::system_clock::now());

I just ran this, and the string contains:

2017-03-30 17:05:13.400455

That's right, it even gives you the full precision. If you don't like that format, all of the strftime formatting flags are available. If you want your local time, there is a timezone library also available, though it is not header only.

std::string s = date::format("%F %T %Z", date::make_zoned(date::current_zone(),
                                         std::chrono::system_clock::now()));

Output:

2017-03-30 13:05:13.400455 EDT

Answer 2

A simpler solution using std::chrono:

#include <chrono>

using sysclock_t = std::chrono::system_clock;

std::string CurrentDate()
{
    std::time_t now = sysclock_t::to_time_t(sysclock_t::now());

    char buf[16] = { 0 };
    std::strftime(buf, sizeof(buf), "%Y-%m-%d", std::localtime(&now));
    
    return std::string(buf);
}

Remember to adjust the format as appropriate for the time too.

Note, however, that I suspect this will not work well for multithreaded code since std::localtime() returns a pointer to an internal struct.