Initialize your now variable.

time_t now = time(0); // Get the system time

The localtime function is used to convert the time value in the passed time_t to a struct tm, it doesn't actually retrieve the system time.

Copy-pasted from here:

/* localtime example */
#include <stdio.h>
#include <time.h>


int main ()
{
time_t rawtime;
struct tm * timeinfo;


time ( &rawtime );
timeinfo = localtime ( &rawtime );
printf ( "Current local time and date: %s", asctime (timeinfo) );
  

return 0;
}

(just add void to the main() arguments list in order for this to work in C)

Easy way:

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


int main(void)
{
time_t mytime = time(NULL);
char * time_str = ctime(&mytime);
time_str[strlen(time_str)-1] = '\0';
printf("Current Time : %s\n", time_str);


return 0;
}

guys i got a new way get system time. though its lengthy and is full of silly works but in this way you can get system time in integer format.

#include <stdio.h>
#include <stdlib.h>


int main()
{
FILE *fp;
char hc1,hc2,mc1,mc2;
int hi1,hi2,mi1,mi2,hour,minute;
system("echo %time% >time.txt");
fp=fopen("time.txt","r");
if(fp==NULL)
exit(1) ;
hc1=fgetc(fp);
hc2=fgetc(fp);
fgetc(fp);
mc1=fgetc(fp);
mc2=fgetc(fp);
fclose(fp);
remove("time.txt");
hi1=hc1;
hi2=hc2;
mi1=mc1;
mi2=mc2;
hi1-=48;
hi2-=48;
mi1-=48;
mi2-=48;
hour=hi1*10+hi2;
minute=mi1*10+mi2;
printf("Current time is %d:%d\n",hour,minute);
return 0;
}

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


void main()
{
time_t t;
time(&t);
clrscr();


printf("Today's date and time : %s",ctime(&t));
getch();
}

To extend the answer from @mingos above, I wrote the below function to format my time to a specific format ([dd mm yyyy hh:mm:ss]).

// Store the formatted string of time in the output
void format_time(char *output){
time_t rawtime;
struct tm * timeinfo;
    

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

sprintf(output, "[%d %d %d %d:%d:%d]", timeinfo->tm_mday,
timeinfo->tm_mon + 1, timeinfo->tm_year + 1900,
timeinfo->tm_hour, timeinfo->tm_min, timeinfo->tm_sec);
}

More information about struct tm can be found here.

You can use this function to get current local time. if you want gmt then use the gmtime function instead of localtime. cheers

time_t my_time;
struct tm * timeinfo;
time (&my_time);
timeinfo = localtime (&my_time);
CCLog("year->%d",timeinfo->tm_year+1900);
CCLog("month->%d",timeinfo->tm_mon+1);
CCLog("date->%d",timeinfo->tm_mday);
CCLog("hour->%d",timeinfo->tm_hour);
CCLog("minutes->%d",timeinfo->tm_min);
CCLog("seconds->%d",timeinfo->tm_sec);

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


void main()
{
time_t t;
time(&t);
printf("\n current time is : %s",ctime(&t));
}

If you just need the time without the date.

  time_t rawtime;
struct tm * timeinfo;
time( &rawtime );
timeinfo = localtime( &rawtime );
printf("%02d:%02d:%02d", timeinfo->tm_hour, timeinfo->tm_min,
timeinfo->tm_sec);

LONG VERSION

src: https://en.wikipedia.org/wiki/C_date_and_time_functions

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


int main(void)
{
time_t current_time;
char* c_time_string;


/* Obtain current time. */
current_time = time(NULL);


if (current_time == ((time_t)-1))
{
(void) fprintf(stderr, "Failure to obtain the current time.\n");
exit(EXIT_FAILURE);
}


/* Convert to local time format. */
c_time_string = ctime(&current_time);


if (c_time_string == NULL)
{
(void) fprintf(stderr, "Failure to convert the current time.\n");
exit(EXIT_FAILURE);
}


/* Print to stdout. ctime() has already added a terminating newline character. */
(void) printf("Current time is %s", c_time_string);
exit(EXIT_SUCCESS);
}

The output is:

Current time is Thu Sep 15 21:18:23 2016

SHORT VERSION:

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


int main(int argc, char *argv[]) {
time_t current_time;
time(&current_time);
printf("%s", ctime(&current_time));

The output is:

Current time is Thu Jan 28 15:22:31 2021

It is recommonded to use localtime_s instead of localtime. This should work.

time_t current_raw_time = time(0); // System time: number of seconds since 00:00, Jan 1 1970 UTC
struct tm day_time;
localtime_s(&day_time, &current_raw_time);

day_time will have the following members:

struct tm
{
int tm_sec;   // seconds after the minute - [0, 60] including leap second
int tm_min;   // minutes after the hour - [0, 59]
int tm_hour;  // hours since midnight - [0, 23]
int tm_mday;  // day of the month - [1, 31]
int tm_mon;   // months since January - [0, 11]
int tm_year;  // years since 1900
int tm_wday;  // days since Sunday - [0, 6]
int tm_yday;  // days since January 1 - [0, 365]
int tm_isdst; // daylight savings time flag
};

Note that, localtime does not provide milliseconds.