ctime(3c)
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ctime, localtime, gmtime, asctime, tzset
convert date and time to string
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SYNTAX
#include <time.h>
char *ctime (clock)
long *clock;
struct tm *localtime (clock)
long *clock;
struct tm *gmtime (clock)
long *clock;
char *asctime (tm)
struct tm *tm;
extern long timezone;
extern int daylight;
extern char *tzname[2];
void tzset ( )
DESCRIPTION
Ctime converts a long integer, pointed to by clock, representing
the time in seconds since 00:00:00 GMT, January 1, 1970, 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 tm structures, described
below. Localtime corrects for the time zone and possible
Daylight Savings Time; gmtime converts directly to Greenwich Mean
Time (GMT), which is the time the DG/UX system uses.
Asctime converts a tm structure to a 26-character string, as
shown in the above example, and returns a pointer to the string.
Declarations of all the functions and externals, and the tm
structure, are in the <time.h> header file. The structure
declaration is:
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ctime(3c)
struct tm {
int tm_sec; /* seconds (0 - 59) */
int tm_min; /* minutes (0 - 59) */
int tm_hour; /* hours (0 - 23) */
int tm_mday; /* day of month (1 - 31) */
int tm_mon; /* month of year (0 - 11) */
int tm_year; /* year - 1900 */
int tm_wday; /* day of week (Sunday = 0) */
int tm_yday; /* day of year (0 - 365) */
int tm_isdst;
};
Tm_isdst is non-zero if Daylight Savings Time is in effect.
The external long variable timezone contains the difference, in
seconds, between GMT and local standard time (in EST, timezone is
5*60*60); the external variable daylight is non-zero if and only
if the standard U.S.A. Daylight Savings Time conversion should
be applied. The program knows about the peculiarities of this
conversion in 1974 and 1975; if necessary, a table for these
years can be extended.
If an environment variable named TZ is present, asctime uses the
contents of the variable to override the default time zone. The
value of TZ must be a three-letter time zone name, followed by a
number representing the difference between local time and
Greenwich Mean Time in hours, followed by an optional three-
letter name for a daylight time zone. For example, the setting
for New Jersey would be EST5EDT. Thus, setting TZ changes the
values of the external variables timezone and daylight; in
addition, the time zone names contained in the external variable:
char *tzname[2] = { "EST", "EDT" };
are set from the environment variable TZ. The function tzset
sets these external variables from TZ; tzset is called by
asctime. The user can also call it.
Note that in most installations, TZ is set by default when the
user logs on, to a value in the local /etc/profile file (see
profile(4)).
Time(2) is quite useful for producing the values with which to
call ctime(3C).
SEE ALSO
time(2), getenv(3C), profile(4), environ(5).
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ctime(3c)
Caveat
The return values point to static data whose content is
overwritten by each call.
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