CTIME(3)
NAME
asctime, ctime, gmtime, localtime, mktime - transform
binary date and time to ASCII
SYNOPSIS
#include <<time.h>>
char *asctime(const struct tm *timeptr);
char *ctime(const time_t *timep);
struct tm *gmtime(const time_t *timep);
struct tm *localtime(const time_t *timep);
time_t mktime(struct tm *timeptr);
extern char *tzname[2];
long int timezone;
extern int daylight;
DESCRIPTION
The ctime(), gmtime() and localtime() functions all take
an argument of data type time_t which represents calendar
time. When interpreted as an absolute time value, it rep-
resents the number of seconds elapsed since 00:00:00 on
January 1, 1970, Coordinated Universal Time (UTC).
The asctime() and mktime() functions both take an argument
representing broken-down time which is a binary represen-
tation separated into year, month, day, etc. Broken-down
time is stored in the structure tm which is defined in
<time.h> as follows:
struct tm
{
int tm_sec; /* seconds */
int tm_min; /* minutes */
int tm_hour; /* hours */
int tm_mday; /* day of the month */
int tm_mon; /* month */
int tm_year; /* year */
int tm_wday; /* day of the week */
int tm_yday; /* day in the year */
int tm_isdst; /* daylight saving time */
};
The members of the tm structure are:
tm_sec The number of seconds after the minute, normally in
the range 0 to 59, but can be up to 61 to allow for
leap seconds.
tm_min The number of minutes after the hour, in the range
0 to 59.
tm_hour
The number of hours past midnight, in the range 0
to 23.
tm_mday
The day of the month, in the range 1 to 31.
tm_mon The number of months since January, in the range 0
to 11.
tm_year
The number of years since 1900.
tm_wday
The number of days since Sunday, in the range 0 to
6.
tm_yday
The number of days since January 1, in the range 0
to 365.
tm_isdst
A flag that indicates whether daylight saving time
is in effect at the time described. The value is
positive if daylight saving time is in effect, zero
if it is not, and negative if the information is
not available.
The ctime() function converts the calendar time timep into
a string of the form
"Wed Jun 30 21:49:08 1993\n"
The abbreviations for the days of the week are `Sun',
`Mon', `Tue', `Wed', `Thu', `Fri', and `Sat'. The abbre-
viations for the months are `Jan', `Feb', `Mar', `Apr',
`May', `Jun', `Jul', `Aug', `Sep', `Oct', `Nov', and
`Dec'. The return value points to a statically allocated
string which might be overwritten by subsequent calls to
any of the date and time functions. The function also
sets the external variable tzname with information about
the current time zone.
The gmtime() function converts the calendar time timep to
broken-down time representation, expressed in Coordinated
Universal Time (UTC).
The localtime() function converts the calendar time timep
to broken-time representation, expressed relative to the
user's specified time zone. The function sets the
external variables tzname with information about the cur-
rent time zone, timezone with the difference between
Coordinated Universal Time (UTC) and local standard time
in seconds, and daylight to a non-zero value if standard
US daylight savings time rules apply.
The asctime() function converts the broken-down time value
timeptr into a string with the same format as ctime().
The return value points to a statically allocated string
which might be overwritten by subsequent calls to any of
the date and time functions.
The mktime() function converts a broken-down time struc-
ture, expressed as local time, to calendar time represen-
tation. The function ignores the specified contents of
the structure members tm_wday and tm_yday and recomputes
them from the other information in the broken-down time
structure. Calling mktime() also sets the external vari-
able tzname with information about the current time zone.
If the specified broken-down time cannot be represented as
calendar time, mktime() returns a value of (time_t)(-1)
and does not alter the tm_wday and tm_yday members of the
broken-down time structure.
CONFORMING TO
SVID 3, POSIX, BSD 4.3, ISO 9899
SEE ALSO
date(1) gettimeofday(2) time(2) tzset(3) difftime(3)
strftime(3) newctime(3).