char *ctime(clock)  long *clock; 

 #include <time.h> 

 struct tm *localtime(clock)  long *clock; 

 struct tm *gmtime(clock)  long *clock; 

 char *asctime(tm)  struct tm *tm; 

 char *timezone(zone, dst) 

Sun Sep 16 01:03:52 1973\\n\\0

Localtime and gmtime return pointers to structures containing the broken-down time. Localtime corrects for the time zone and possible daylight savings time; gmtime converts directly to GMT, which is the time UNIX uses. Asctime converts a broken-down time to ASCII and returns a pointer to a 26-character string.

The structure declaration from the include file is:

.nr .0 .8i+\w'int tm_isdst'u
struct tm {
 int tm_sec; /* 0-59 seconds */
 int tm_min; /* 0-59 minutes */
 int tm_hour; /* 0-23 hour */
 int tm_mday; /* 1-31 day of month */
 int tm_mon; /* 0-11 month */
 int tm_year; /* 0- year - 1900 */
 int tm_wday; /* 0-6 day of week (Sunday = 0) */
 int tm_yday; /* 0-365 day of year */
 int tm_isdst; /* flag: daylight savings time in effect */
};

When local time is called for, the program consults the system to determine the time zone and whether the U.S.A., Australian, Eastern European, Middle European, or Western European daylight saving time adjustment is appropriate. The program knows about various peculiarities in time conversion over the past 10-20 years; if necessary, this understanding can be extended.

Timezone returns the name of the time zone associated with its first argument, which is measured in minutes westward from Greenwich. If the second argument is 0, the standard name is used, otherwise the Daylight Saving version. If the required name does not appear in a table built into the routine, the difference from GMT is produced; e.g. in Afghanistan timezone(-(60*4+30), 0) is appropriate because it is 4:30 ahead of GMT and the string GMT+4:30 is produced.