How to get the date and time values in a C program?

I have something like this:

char *current_day, *current_time;
system("date +%F");
system("date +%T");

It prints the current day and time in the stdout, but I want to get this output or assign them to the current_day and current_time variables, so that I can do some processing with those values later on.

current_day ==> current day
current_time ==> current time

The only solution that I can think of now is to direct the output to some file, and then read the file and then assign the values of date and time to current_day and current_time. But I think this is not a good way. Is there any other short and elegant way?

Use time() and localtime() to get the time:

#include <stdio.h>
#include <time.h>

int main()
{
  time_t t = time(NULL);
  struct tm tm = *localtime(&t);
  printf("now: %d-%02d-%02d %02d:%02d:%02d\n", tm.tm_year + 1900, tm.tm_mon + 1, tm.tm_mday, tm.tm_hour, tm.tm_min, tm.tm_sec);
}

strftime (C89)

Martin mentioned it, here's an example:

main.c

#include <assert.h>
#include <stdio.h>
#include <time.h>

int main(void) {
    time_t t = time(NULL);
    struct tm *tm = localtime(&t);
    char s[64];
    assert(strftime(s, sizeof(s), "%c", tm));
    printf("%s\n", s);
    return 0;
}

GitHub upstream.

Compile and run:

gcc -std=c89 -Wall -Wextra -pedantic -o main.out main.c
./main.out

Sample output:

Thu Apr 14 22:39:03 2016

The %c specifier produces the same format as ctime.

One advantage of this function is that it returns the number of bytes written, allowing for better error control in case the generated string is too long:

RETURN VALUE

Provided that the result string, including the terminating null byte, does not exceed max bytes, strftime() returns the number of bytes (excluding the terminating null byte) placed in the array s. If the length of the result string (including the terminating null byte) would exceed max bytes, then strftime() returns 0, and the contents of the array are undefined.

Note that the return value 0 does not necessarily indicate an error. For example, in many locales %p yields an empty string. An empty format string will likewise yield an empty string.

asctime and ctime (C89, deprecated in POSIX 7)

asctime is a convenient way to format a struct tm:

main.c

#include <stdio.h>
#include <time.h>

int main(void) {
    time_t t = time(NULL);
    struct tm *tm = localtime(&t);
    printf("%s", asctime(tm));
    return 0;
}

Sample output:

Wed Jun 10 16:10:32 2015

And there is also ctime() which the standard says is a shortcut for:

asctime(localtime())

As mentioned by Jonathan Leffler, the format has the shortcoming of not having timezone information.

POSIX 7 marked those functions as "obsolescent" so they could be removed in future versions:

The standard developers decided to mark the asctime() and asctime_r() functions obsolescent even though asctime() is in the ISO C standard due to the possibility of buffer overflow. The ISO C standard also provides the strftime() function which can be used to avoid these problems.

C++ version of this question: How to get current time and date in C++?

Tested in Ubuntu 16.04.

How to get the date and time values in a C program?

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