C library - asctime() function

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The C library asctime() function returns a pointer to a string which represents the day and time of the structure struct timeptr. This function is used to represent the calender time into a human-readable string.

Syntax

Following is the syntax of the C Library asctime() function −

char *asctime(const struct tm *timeptr)

Parameters

The timeptr is a pointer to tm structure that contains a calendar time broken down into its components as shown below −

struct tm {
   int tm_sec;         /* seconds,  range 0 to 59          */
   int tm_min;         /* minutes, range 0 to 59           */
   int tm_hour;        /* hours, range 0 to 23             */
   int tm_mday;        /* day of the month, range 1 to 31  */
   int tm_mon;         /* month, range 0 to 11             */
   int tm_year;        /* The number of years since 1900   */
   int tm_wday;        /* day of the week, range 0 to 6    */
   int tm_yday;        /* day in the year, range 0 to 365  */
   int tm_isdst;       /* daylight saving time             */
};

Return Value

This function returns a C string containing the date and time information in a human-readable format Www Mmm dd hh:mm:ss yyyy, where Www is the weekday, Mmm the month in letters, dd the day of the month, hh:mm:ss the time, and yyyy the year.

Example 1

Following is the simple C Library program of asctime() function.

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

int main () {
   struct tm t;

   t.tm_sec    = 10;
   t.tm_min    = 10;
   t.tm_hour   = 6;
   t.tm_mday   = 25;
   t.tm_mon    = 2;
   t.tm_year   = 89;
   t.tm_wday   = 6;

   puts(asctime(&t));
   
   return(0);
}

Output

The above code produces the following result −

Sat Mar 25 06:10:10 1989

Example 2

To obtain the current/local time, we use the localtime() function to generate the local time of the clock and then call the asctime() to display it.

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

int main() {
   struct tm* ptr;
   time_t lt;
   lt = time(NULL);
   ptr = localtime(&lt);
   printf("Current local time: %s", asctime(ptr));
   return 0;
}

Output

On execution of above code, we get the following result −

Current local time: Tue May 14 07:00:11 2024

Example 3

The C program shows the current local time in a human-readable format using the functions &minus asctime() and if available asctime_s().

#define __STDC_WANT_LIB_EXT1__ 1
#include <stdio.h>
#include <time.h>

int main(void) {
    struct tm tm = *localtime(&(time_t){time(NULL)});
    printf("Current local time (using asctime()): %s\n", asctime(&tm));

    #ifdef __STDC_LIB_EXT1__
    char str[50];
    asctime_s(str, sizeof str, &tm);
    printf("Current local time (using asctime_s()): %s\n", str);
    #endif
    return 0;
}

Output

After execution of above code, we get the following result −

Current local time (using asctime()): Tue May 14 07:09:57 2024