Time Conversion Functions

• the tm structure
  • Broken down time is stored in a tm.
  • There are a number of functions that take a tm and do something useful with it

  • struct tm
    {
      int tm_sec;                   /* Seconds.     [0-60] (1 leap second) */
      int tm_min;                   /* Minutes.     [0-59] */
      int tm_hour;                  /* Hours.       [0-23] */
      int tm_mday;                  /* Day.         [1-31] */
      int tm_mon;                   /* Month.       [0-11] */
      int tm_year;                  /* Year - 1900.  */
      int tm_wday;                  /* Day of week. [0-6]  since sunday*/ 
      int tm_yday;                  /* Days in year.[0-365] */
      int tm_isdst;                 /* DST.         [-1/0/1]*/
                                    // > 0 DST is in effect
    				// = 0 DST is not in effect
    				// negative, no time information.
    
    # ifdef __USE_MISC
      long int tm_gmtoff;           /* Seconds east of UTC.  */
      const char *tm_zone;          /* Timezone abbreviation.  */
    # else
      long int __tm_gmtoff;         /* Seconds east of UTC.  */
      const char *__tm_zone;        /* Timezone abbreviation.  */
    # endif
    };
    
    	

  • struct tm *gmtime(const time_t *timep);
  • struct tm *localtime(const time_t *timep);
  • Convert from a time_t to a tm
  • time_t mktime(struct tm *tm);
  • converts from at tm to a time_t
  • These are done in static structures.
  • Localtime uses the local time zone.
  • mktime assumes that the broken down time value is in local time.
• A broken down time structure is then used to produce printable formats
  • char *asctime(const struct tm *tm);
  • This takes a tm and returns a pointer to a string containing a printable time.
  • size_t strftime(char *s, size_t max, const char *format, const struct tm *tm);
  • This takes a tm
  • And a format string
  • And a c style string of a given size.
  • And will return the corresponding date string.
• Look at bdtime.C