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;
}

Solution 1

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;
}

Solution 2

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;
}

Solution 3

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

Solution 4

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;
}

Solution 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;
}

View more solutions

Comments

[Mat]

pubs.opengroup.org/onlinepubs/9699919799/functions/…

[Some programmer dude]

Wouldn't it be simpler to use std::strftime?

[M456]

Boost - Date Time

[maverik]

Here is a question (and answer) about how to do this using boost (if you somehow cannot use C++11):

[Matthieu M.]

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 ?

[Rafael Baptista]

It doesn't take much thinking for any given format string to compute a maximum possible string length.

[Yuriy Petrovskiy]

std::put_time is still missing in gcc 4.9.

[Michael Trouw]

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 : 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?

[max]

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.

[Aconcagua]

No, you can't: asctime does not deliver the date/time format requested in the question!

[SmallChess]

gcc 5.0 has it, but not the earlier versions.

[SmallChess]

@Aconcagua While it doesn't, it does give you time in a string. The code is clean and concise.

[Aconcagua]

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...

[solendil]

Nice answer, but asctime() has the VERY bad idea of returning a LF terminated String...

[scrutari]

To get milliseconds: auto now = std::chrono::system_clock::now(); std::chrono::time_point<std::chrono::system_clock> epoch; int ms = std::chrono::duration_cast<std::chrono::milliseconds>(now - epoch).count() % 1000;

[Admin]

@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?

[awesoon]

@ArnavBorborah, it depends. You may return time in Unix format, Boost Local date time or create your own type.

[Homer6]

localtime is not thread safe. Consider using localtime_r instead.

[Roi Danton]

Furthermore asctime is not locale-sensitive like strftime is.

[Melebius]

Thank you for this code snippet, which might provide some limited, immediate help. A proper explanation 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 #includes.

[Steve Smith]

What does this actually return?

[SimonC]

Sadly this function returns 0 and doesn't format the date/time correctly on Windows 10. (At least for me).

[Ruslan]

@Homer6 it's not standard. See also: Will getting the current date/time be thread-safe in C++20?

[phamuc]

@Steve Smith The output is: Tue Sep 14 14:17:16 2021

[Howard Hinnant]

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.