Get UTC epoch timestamp function

utctimestamp.c

#include <stdio.h>

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

/**
 * This function returns a UTC epoch timestamp based on
 * the supplied time information.
 *
 * @param [in] second  Seconds        [0-59]
 * @param [in] minute  Minutes        [0-59]
 * @param [in] hour    Hours          [0-23]
 * @param [in] date    Day of month   [1-31]
 * @param [in] month   Month          [1-12].
 * @param [in] year    Years          [1970-2335]
 *
 * @retval timestamp   Epoch timestamp in UTC.
 */
time_t utctimestamp(int second, int minute, int hour, int date, int month, int year)
{
  struct tm*  pLocalTm = NULL;
  struct tm   wantedTm;
  time_t      epoch = 0;
  
  
  /* Initialize variables */
  memset(&wantedTm, 0, sizeof(wantedTm));
  
  
  /* Set up time structure */
  wantedTm.tm_sec   = second;
  wantedTm.tm_min   = minute;
  wantedTm.tm_hour  = hour;
  wantedTm.tm_mday  = date;
  wantedTm.tm_mon   = month - 1;
  wantedTm.tm_year  = year - 1900;
  wantedTm.tm_isdst = -1;
  
  
  /* Get the timestamp */
  epoch = mktime(&wantedTm);
  
  
  /* Get local time information */
  pLocalTm = localtime(&epoch);
  
  
  /* Adjust epoch to UTC */
  epoch += pLocalTm->tm_gmtoff;
  
  
  /* Return timestamp */
  return epoch;
}

int main(int argc, char **argv)
{
  printf("Test #1> 1970-01-01 00:00:00 UTC : %lu, %s\n", (unsigned long)utctimestamp(00, 00, 00, 01, 01, 1970), utctimestamp(00, 00, 00, 01, 01, 1970) == 0           ? "PASS" : "FAIL");
  printf("Test #2> 2012-05-10 21:04:33 UTC : %lu, %s\n", (unsigned long)utctimestamp(33, 04, 21, 10, 05, 2012), utctimestamp(33, 04, 21, 10, 05, 2012) == 1336683873  ? "PASS" : "FAIL");
  
  return 0;
}