Listing 1: getutctime.c

/* 
getutctime.c
Print the current value of the system time counter, or if an argument  
of the form hh:mm:ss:m:d:year is specified on the command line, print the 
system clock value for that time.  The program does not do any range 
checking of a user specified date and time.  
*/
     
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <ctype.h>
#include <langinfo.h>
#include <limits.h>
#include <string.h>
     
/* Prototypes */
     
void time_now();
int store_time(char *);
     
/* The tm struct is declared in time.h. */
     
struct tm usertime;
     
void main (int argc, char *argv[]) 
{
  time_t user_supplied_time;
     
  if( argc == 1) 
    {
      time_now();
    }
     
  /* Place the time and date from the command line into the tm struct. */
  if( argc == 2 ) 
    {
      store_time(argv[1]); 
      user_supplied_time = mktime(&usertime); 
      printf("%ld.\n", user_supplied_time);
    }
}
     
int store_time(char *user_time)
{
  const char fmt[18]="%d:%d:%d:%d:%d:%d";
     
/* put the values into the usertime struct */
  sscanf(user_time, fmt, 
         &usertime.tm_hour, 
         &usertime.tm_min,
         &usertime.tm_sec,
         &usertime.tm_mon,
         &usertime.tm_mday,
         &usertime.tm_year );
     
  /* Because mktime counts months starting with 0. */ 
  usertime.tm_mon -= 1;
  /* The counter still doesn't overflow after year 2000. */ 
  usertime.tm_year -= 1900;
  return(0);
}
     
void time_now() 
{
  time_t now;
     
  now = time(NULL);
  printf("%ld.\n", now);
}
     
     
/* End of File */