asctime asctime_r ctime ctime_r difftime gmtime gmtime_r localtime localtime_r mktime timegm - transform binary date and time values
converts the time value pointed at by Fa clock , and returns a pointer to a ``Fa struct tm '' (described below) which contains the broken-out time information for the value after adjusting for the current time zone (and any other factors such as Daylight Saving Time). Time zone adjustments are performed as specified by the TZ environment variable (see tzset(3)). The function localtime ();
uses tzset(3) to initialize time conversion information if tzset(3) has not already been called by the process.
After filling in the tm structure,
sets the Fa tm_isdst Ns 'th element of Fa tzname to a pointer to an ASCII string that is the time zone abbreviation to be used with localtime (Ns 's);
similarly converts the time value, but without any time zone adjustment, and returns a pointer to a tm structure (described below).
function adjusts the time value for the current time zone in the same manner as localtime (,);
and returns a pointer to a 26-character string of the form:
Thu Nov 24 18:22:48 1986\n\0
All the fields have constant width.
function provides the same functionality as ctime ();
except the caller must provide the output buffer Fa buf to store the result, which must be at least 26 characters long. The localtime_r ();
and gmtime_r ();
functions provide the same functionality as localtime ();
and gmtime ();
respectively, except the caller must provide the output buffer Fa result .
function converts the broken down time in the structure Fa tm pointed at by Fa *tm to the form shown in the example above.
function provides the same functionality as asctime ();
except the caller provide the output buffer Fa buf to store the result, which must be at least 26 characters long.
and timegm ();
convert the broken-down time in the structure pointed to by tm into a time value with the same encoding as that of the values returned by the time(3) function (that is, seconds from the Epoch, UTC ) The mktime ();
function interprets the input structure according to the current timezone setting (see tzset(3)). The timegm ();
function interprets the input structure as representing Universal Coordinated Time (UTC )
The original values of the
components of the structure are ignored, and the original values of the
other components are not restricted to their normal ranges, and will be
normalized if needed.
October 40 is changed into November 9,
of -1 means 1 hour before midnight,
of 0 means the day preceding the current month, and
of -2 means 2 months before January of
Fa tm_year .
(A positive or zero value for
to presume initially that summer time (for example, Daylight Saving Time) is or is not in effect for the specified time, respectively. A negative value for Fa tm_isdst causes the mktime ();
function to attempt to divine whether summer time is in effect for the specified time. The Fa tm_isdst and Fa tm_gmtoff members are forced to zero by timegm (. ));
On successful completion, the values of the
components of the structure are set appropriately, and the other components
are set to represent the specified calendar time, but with their values
forced to their normal ranges; the final value of
is not set until
function returns the specified calendar time; if the calendar time cannot be represented, it returns -1;
function returns the difference between two calendar times, ( Fa time1 - Fa time0 ) , expressed in seconds.
External declarations as well as the tm structure definition are in the
include file. The tm structure includes at least the following fields:
int tm_sec; /* seconds (0 - 60) */ 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; /* is summer time in effect? */ char *tm_zone; /* abbreviation of timezone name */ long tm_gmtoff; /* offset from UTC in seconds */
The field Fa tm_isdst is non-zero if summer time is in effect.
The field Fa tm_gmtoff is the offset (in seconds) of the time represented from UTC with positive values indicating east of the Prime Meridian.
and localtime_r ();
functions are expected to conform to St -p1003.1-96 (again provided the selected local timezone does not contain a leap-second table).
function is not specified by any standard; its function cannot be completely emulated using the standard functions described above.
The C Standard provides no mechanism for a program to modify its current local timezone setting, and the POSIX -standard method is not reentrant. (However, thread-safe implementations are provided in the POSIX threaded environment.)
The tm_zone field of a returned Vt tm structure points to a static array of characters, which will also be overwritten by any subsequent calls (as well as by subsequent calls to tzset(3) and tzsetwall(3)).
Use of the external variable Fa tzname is discouraged; the Fa tm_zone entry in the tm structure is preferred.
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Created 1996-2023 by Maxim Chirkov
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