NAME

ctime, localtime, gmtime, asctime, timezone −  convert date and time to ASCII

SYNOPSIS

char ∗ctime(clock)
long ∗clock;

#include <sys/time.h>

struct tm ∗localtime(clock)
long ∗clock;

struct tm ∗gmtime(clock)
long ∗clock;

char ∗asctime(tm)
struct tm ∗tm;

char ∗timezone(zone, dst)

DESCRIPTION

Ctime converts a time pointed to by clock such as returned by time(2) into ASCII and returns a pointer to a 26-character string in the following form. All the fields have constant width.

    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:

struct tm {
inttm_sec;
inttm_min;
inttm_hour;
inttm_mday;
inttm_mon;
inttm_year;
inttm_wday;
inttm_yday;
inttm_isdst;
};

These quantities give the time on a 24-hour clock, day of month (1-31), month of year (0-11), day of week (Sunday = 0), year − 1900, day of year (0-365), and a flag that is nonzero if daylight saving time is 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. 

SEE ALSO

gettimeofday(2), time(3)

BUGS

The return values point to static data whose content is overwritten by each call. 

4th Berkeley Distribution  —  1 August 1985