Parsing the time function under Linux: how to set and get the time

time_t time(time_t *t);
char *asctime(const struct tm *tm);
char *asctime_r(const struct tm *tm, char *buf);
char *ctime(const time_t *timep);
char *ctime_r(const time_t *timep, char *buf);
struct tm *gmtime(const time_t *timep); //Acquired for British time
struct tm *gmtime_r(const time_t *timep, struct tm *result);
struct tm *localtime(const time_t *timep);      //Local time. Note the difference between British time and local time.
struct tm *localtime_r(const time_t *timep, struct tm *result);
time_t mktime(struct tm *tm);
double difftime(time_t time1, time_t time0);
int gettimeofday(struct timeval *tv, struct timezone *tz);
int settimeofday(const struct timeval *tv , const struct timezone *tz);

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

int main(void)
{
time_t t1;
time_t t2;
struct tm *my_tm;
char buf[128] = {0};

//Number of seconds since Epoch (00:00:00 UTC, January 1,1970)
t1 = time(&t1);
printf("%dn", t1);  //1355905754
t2 = time(&t2);
sleep(1);
printf("%lfn", difftime(t2, t1));  //The difference between t1 and t2 is 1.000000. Sometimes this function can be used as a pseudo-timer
printf("%sn",ctime(&t1)); //Wed Dec 19 16:29:14 2012
      
//init tm
my_tm->tm_year = 2012-1900;
my_tm->tm_mon = 12-1;
my_tm->tm_mday = 12;
my_tm->tm_hour = 12;
my_tm->tm_min = 12;
my_tm->tm_sec = 12;
      //Set a time
t1 = mktime(my_tm);
//Get time 
my_tm = localtime(&t1);
sprintf(buf, "%04d-%02d-%02d  %02d:%02d:%02d",
my_tm->tm_year + 1900, my_tm->tm_mon + 1, my_tm->tm_mday, my_tm->tm_hour, my_tm->tm_min, my_tm->tm_sec);
printf("%sn", buf);//2012-12-12  12:12:12

return 0;
}