/* TIMES.C illustrates various time and date functions including:
 *      time            _ftime          ctime       asctime
 *      localtime       gmtime          mktime      _tzset
 *      _strtime        _strdate        strftime
 *
 * Also the global variable:
 *      _tzname
 */

#include <time.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/timeb.h>
#include <string.h>

void main()
{
    char tmpbuf[ 128 ], ampm[] = "AM";
    time_t ltime;
    struct _timeb tstruct;
    struct tm *today, *gmt, xmas = {  0 ,  0 ,  12 ,  25 ,  11 ,  93  };

    /* Set time zone from TZ environment variable. If TZ is not set,
     * the operating system is queried to obtain the default value 
     * for the variable. 
     */
    _tzset();

    /* Display operating system-style date and time. */
    _strtime( tmpbuf );
    printf( "OS time:\t\t\t\t%s\n", tmpbuf );
    _strdate( tmpbuf );
    printf( "OS date:\t\t\t\t%s\n", tmpbuf );

    /* Get UNIX-style time and display as number and string. */
    time( &ltime );
    printf( "Time in seconds since UTC 1/1/70:\t%ld\n", ltime );
    printf( "UNIX time and date:\t\t\t%s", ctime( &ltime ) );

    /* Display UTC. */
    gmt = gmtime( &ltime );
    printf( "Coordinated universal time:\t\t%s", asctime( gmt ) );

    /* Convert to time structure and adjust for PM if necessary. */
    today = localtime( &ltime );
    if( today->tm_hour >  12  )
    {
   strcpy( ampm, "PM" );
   today->tm_hour -=  12 ;
    }
    if( today->tm_hour ==  0  )  /* Adjust if midnight hour. */
   today->tm_hour =  12 ;

    /* Note how pointer addition is used to skip the first 11 
     * characters and printf is used to trim off terminating 
     * characters.
     */
    printf( "12-hour time:\t\t\t\t%.8s %s\n",
       asctime( today ) +  11 , ampm );

    /* Print additional time information. */
    _ftime( &tstruct );
    printf( "Plus milliseconds:\t\t\t%u\n", tstruct.millitm );
    printf( "Zone difference in seconds from UTC:\t%u\n", 
             tstruct.timezone );
    printf( "Time zone name:\t\t\t\t%s\n", _tzname[ 0 ] );
    printf( "Daylight savings:\t\t\t%s\n", 
             tstruct.dstflag ? "YES" : "NO" );

    /* Make time for noon on Christmas, 1993. */
    if( mktime( &xmas ) != (time_t)- 1  )
   printf( "Christmas\t\t\t\t%s\n", asctime( &xmas ) );

    /* Use time structure to build a customized time string. */
    today = localtime( &ltime );

    /* Use strftime to build a customized time string. */
    strftime( tmpbuf,  128 ,
         "Today is %A, day %d of %B in the year %Y.\n", today );
    printf( tmpbuf );
}



Output

OS time:                                 21 : 51 : 03 
OS date:                                 05 / 03 / 94 
Time in seconds since UTC  1 / 1 / 70 :        768027063 
UNIX time and date:                     Tue May  03   21 : 51 : 03   1994 
Coordinated universal time:             Wed May  04   04 : 51 : 03   1994 
 12 -hour time:                            09 : 51 : 03  PM
Plus milliseconds:                       279 
Zone difference in seconds from UTC:     480 
Time zone name:                         
Daylight savings:                       YES
Christmas                               Sat Dec  25   12 : 00 : 00   1993 

Today is Tuesday, day  03  of May in the year  1994 .