Current date and time as string

Question

I wrote a function to get a current date and time in format: DD-MM-YYYY HH:MM:SS. It works but let's say, its pretty ugly. How can I do exactly the same thing but simpler?

string currentDateToString()
{
    time_t now = time(0);
    tm *ltm = localtime(&now);

    string dateString = "", tmp = "";
    tmp = numToString(ltm->tm_mday);
    if (tmp.length() == 1)
        tmp.insert(0, "0");
    dateString += tmp;
    dateString += "-";
    tmp = numToString(1 + ltm->tm_mon);
    if (tmp.length() == 1)
        tmp.insert(0, "0");
    dateString += tmp;
    dateString += "-";
    tmp = numToString(1900 + ltm->tm_year);
    dateString += tmp;
    dateString += " ";
    tmp = numToString(ltm->tm_hour);
    if (tmp.length() == 1)
        tmp.insert(0, "0");
    dateString += tmp;
    dateString += ":";
    tmp = numToString(1 + ltm->tm_min);
    if (tmp.length() == 1)
        tmp.insert(0, "0");
    dateString += tmp;
    dateString += ":";
    tmp = numToString(1 + ltm->tm_sec);
    if (tmp.length() == 1)
        tmp.insert(0, "0");
    dateString += tmp;

    return dateString;
}

http://pubs.opengroup.org/onlinepubs/9699919799/functions/strftime.html — Mat, May 03 '13 at 11:37
Wouldn't it be simpler to use [`std::strftime`](http://en.cppreference.com/w/cpp/chrono/c/strftime)? — Some programmer dude, May 03 '13 at 11:38
[Boost - Date Time](http://www.boost.org/doc/libs/1_53_0/doc/html/date_time/examples.html#date_time.examples.dates_as_strings) — M456, May 03 '13 at 11:40
Here is a [question](http://stackoverflow.com/questions/5018188/how-to-format-a-datetime-to-string-using-boost) (and answer) about how to do this using boost (if you somehow cannot use C++11): — maverik, May 03 '13 at 11:46

awesoon · Answer 1 · 2022-06-08T19:22:04.047

208

Since C++11 you could use std::put_time from iomanip header:

#include <iostream>
#include <iomanip>
#include <ctime>

int main()
{
    auto t = std::time(nullptr);
    auto tm = *std::localtime(&t);
    std::cout << std::put_time(&tm, "%d-%m-%Y %H-%M-%S") << std::endl;
}

std::put_time is a stream manipulator, therefore it could be used together with std::ostringstream in order to convert the date to a string:

#include <iostream>
#include <iomanip>
#include <ctime>
#include <sstream>

int main()
{
    auto t = std::time(nullptr);
    auto tm = *std::localtime(&t);

    std::ostringstream oss;
    oss << std::put_time(&tm, "%d-%m-%Y %H-%M-%S");
    auto str = oss.str();

    std::cout << str << std::endl;
}

edited Jun 08 '22 at 19:22

answered May 03 '13 at 11:42

awesoon

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35

`std::put_time` is still missing in gcc 4.9. – Yuriy Petrovskiy Aug 15 '14 at 21:30
5

gcc 5.0 has it, but not the earlier versions. – ABCD Jul 14 '15 at 02:15
@soon I have a question. In my code, I have a function that is supposed to return a time. What should be the return type of a function, that returns the current time? – Sep 18 '16 at 15:57
@ArnavBorborah, it depends. You may return time in [Unix format](https://en.wikipedia.org/wiki/Unix_time), [Boost Local date time](http://www.boost.org/doc/libs/1_61_0/doc/html/date_time/local_time.html#date_time.local_time.local_date_time) or create your own type. – awesoon Sep 18 '16 at 16:06
localtime is not thread safe. Consider using localtime_r instead. – Homer6 Dec 26 '16 at 20:56
@Homer6 it's not standard. See also: [Will getting the current date/time be thread-safe in C++20?](https://stackoverflow.com/q/48106291/673852) – Ruslan Nov 20 '19 at 18:34

score 140 · Accepted Answer · edited Aug 24 '18 at 00:40

140

Non C++11 solution: With the <ctime> header, you could use strftime. Make sure your buffer is large enough, you wouldn't want to overrun it and wreak havoc later.

#include <iostream>
#include <ctime>

int main ()
{
  time_t rawtime;
  struct tm * timeinfo;
  char buffer[80];

  time (&rawtime);
  timeinfo = localtime(&rawtime);

  strftime(buffer,sizeof(buffer),"%d-%m-%Y %H:%M:%S",timeinfo);
  std::string str(buffer);

  std::cout << str;

  return 0;
}

edited Aug 24 '18 at 00:40

xuhdev

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answered May 03 '13 at 11:50

max

4,248
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3

And what if it overflows the buffer ? I suppose there should be a return value to `strftime` that you need to inspect in real code no ? – Matthieu M. May 03 '13 at 12:17
6

It doesn't take much thinking for any given format string to compute a maximum possible string length. – Rafael Baptista May 03 '13 at 13:05
1

I don't understand why you can pass rawtime by value on the 10th line from the top, as time acceps a pointer to a time_t type : http://www.cplusplus.com/reference/ctime/time/ In the example on that page they used time() the same way which i don't understand. Can anyone explain me this? – Michahell Jan 28 '15 at 14:23
1

There's an `&` there. That means instead of the contents of the `rawtime` variable, it's address in memory will be passed... which is what is stored in a pointer variable. – max Jan 30 '15 at 04:57
To get milliseconds: auto now = std::chrono::system_clock::now(); std::chrono::time_point epoch; int ms = std::chrono::duration_cast(now - epoch).count() % 1000; – scrutari Apr 27 '16 at 10:56
Sadly this function returns 0 and doesn't format the date/time correctly on Windows 10. (At least for me). – SimonC May 29 '19 at 07:15

score 29 · Answer 3 · edited Oct 16 '15 at 02:35

29

you can use asctime() function of time.h to get a string simply .

time_t _tm =time(NULL );

struct tm * curtime = localtime ( &_tm );
cout<<"The current date/time is:"<<asctime(curtime);

Sample output:

The current date/time is:Fri Oct 16 13:37:30 2015

edited Oct 16 '15 at 02:35

ABCD

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answered May 03 '13 at 11:48

birubisht

890
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3

No, you can't: asctime does not deliver the date/time format requested in the question! – Aconcagua Feb 02 '15 at 15:44
3

@Aconcagua While it doesn't, it does give you time in a string. The code is clean and concise. – ABCD Oct 16 '15 at 02:36
5

Clean and concise code does not help if it does not provide what one wants or needs. Want a truck (string), you get one. Wanting to transport liquids, you need a tanker truck and won't be happy getting a dump truck... – Aconcagua Oct 16 '15 at 07:47
4

Nice answer, but asctime() has the VERY bad idea of returning a LF terminated String... – solendil Nov 09 '15 at 10:56
1

Furthermore `asctime` is not locale-sensitive like `strftime` is. – Roi Danton Aug 01 '17 at 08:51

score 17 · Answer 4 · answered Dec 13 '21 at 09:26

17

With C++20, time point formatting (to string) is available in the (chrono) standard library. https://en.cppreference.com/w/cpp/chrono/system_clock/formatter

#include <chrono>
#include <format>
#include <iostream>

int main()
{
   const auto now = std::chrono::system_clock::now();
   std::cout << std::format("{:%d-%m-%Y %H:%M:%OS}", now) << '\n';
}

Output

13-12-2021 09:24:44

It works in Visual Studio 2019 (v16.11.5) with the latest C++ language version (/std:c++latest).

answered Dec 13 '21 at 09:26

Synck

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Clarification: This gives the current UTC time, whereas the OP appears to want the current local time according to his computer's currently set time zone. This is also easy in C++20. – Howard Hinnant Jun 08 '22 at 17:49

score 7 · Answer 5 · answered Oct 26 '17 at 00:12

Using C++ in MS Visual Studio 2015 (14), I use:

#include <chrono>

string NowToString()
{
  chrono::system_clock::time_point p = chrono::system_clock::now();
  time_t t = chrono::system_clock::to_time_t(p);
  char str[26];
  ctime_s(str, sizeof str, &t);
  return str;
}

score 5 · Answer 6 · edited May 06 '20 at 07:24

5

#include <chrono>
#include <iostream>

int main()
{
    std::time_t ct = std::time(0);
    char* cc = ctime(&ct);

    std::cout << cc << std::endl;
    return 0;
}

edited May 06 '20 at 07:24

Steve Lautenschlager

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answered Sep 13 '18 at 11:55

AGG GAA

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Thank you for this code snippet, which might provide some limited, immediate help. A [proper explanation](https://meta.stackexchange.com/q/114762/349538) would greatly improve its long-term value by showing why this is a good solution to the problem and would make it more useful to future readers with other, similar questions. Please [edit] your answer to add some explanation, including the assumptions you’ve made, like `#include`s. – Melebius Sep 13 '18 at 12:29
3

What does this actually return? – Steve Smith Sep 18 '18 at 10:53
@Steve Smith The output is: Tue Sep 14 14:17:16 2021 – phamuc Sep 14 '21 at 12:18

score 2 · Answer 7 · edited May 23 '17 at 11:54

I wanted to use the C++11 answer, but I could not because GCC 4.9 does not support std::put_time.

std::put_time implementation status in GCC?

I ended up using some C++11 to slightly improve the non-C++11 answer. For those that can't use GCC 5, but would still like some C++11 in their date/time format:

 std::array<char, 64> buffer;
 buffer.fill(0);
 time_t rawtime;
 time(&rawtime);
 const auto timeinfo = localtime(&rawtime);
 strftime(buffer.data(), sizeof(buffer), "%d-%m-%Y %H-%M-%S", timeinfo);
 std::string timeStr(buffer.data());

Current date and time as string

7 Answers7

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