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All Rights Reserved. .\" Copyright (c) 2003, Sun Microsystems, Inc. All Rights Reserved. .\" Copyright 2016 Joyent, Inc. .\" .TH MKTIME 3C "Mar 14, 2016" .SH NAME mktime, timegm \- convert a tm structure to a calendar time .SH SYNOPSIS .LP .nf #include \fBtime_t\fR \fBmktime\fR(\fBstruct tm *\fR\fItimeptr\fR); .fi .LP .nf \fBtime_t\fR \fBtimegm\fR(\fBstruct tm *\fR\fItimeptr\fR); .fi .SH DESCRIPTION .LP The \fBmktime()\fR function converts the time represented by the \fBtm\fR structure pointed to by \fItimeptr\fR into a calendar time (the number of seconds since 00:00:00 UTC, January 1, 1970). .sp .LP The \fBtm\fR structure contains the following members: .sp .in +2 .nf int tm_sec; /* seconds after the minute [0, 60] */ int tm_min; /* minutes after the hour [0, 59] */ int tm_hour; /* hour since midnight [0, 23] */ int tm_mday; /* day of the month [1, 31] */ int tm_mon; /* months since January [0, 11] */ int tm_year; /* years since 1900 */ int tm_wday; /* days since Sunday [0, 6] */ int tm_yday; /* days since January 1 [0, 365] */ int tm_isdst; /* flag for daylight savings time */ .fi .in -2 .sp .LP In addition to computing the calendar time, \fBmktime()\fR normalizes the supplied \fBtm\fR structure. The original values of the \fBtm_wday\fR and \fBtm_yday\fR components of the structure are ignored, and the original values of the other components are not restricted to the ranges indicated in the definition of the structure. On successful completion, the values of the \fBtm_wday\fR and \fBtm_yday\fR components are set appropriately, and the other components are set to represent the specified calendar time, but with their values forced to be within the appropriate ranges. The final value of \fBtm_mday\fR is not set until \fBtm_mon\fR and \fBtm_year\fR are determined. .sp .LP The \fBtm_year\fR member must be for year 1901 or later. Calendar times before 20:45:52 UTC, December 13, 1901 or after 03:14:07 UTC, January 19, 2038 cannot be represented. Portable applications should not try to create dates before 00:00:00 UTC, January 1, 1970 or after 00:00:00 UTC, January 1, 2038. .sp .LP The original values of the components may be either greater than or less than the specified range. For example, a \fBtm_hour\fR of \(mi1 means 1 hour before midnight, \fBtm_mday\fR of 0 means the day preceding the current month, and \fBtm_mon\fR of \(mi2 means 2 months before January of \fBtm_year\fR. .sp .LP If \fBtm_isdst\fR is positive, the original values are assumed to be in the alternate timezone. If it turns out that the alternate timezone is not valid for the computed calendar time, then the components are adjusted to the main timezone. Likewise, if \fBtm_isdst\fR is zero, the original values are assumed to be in the main timezone and are converted to the alternate timezone if the main timezone is not valid. If \fBtm_isdst\fR is negative, \fBmktime()\fR attempts to determine whether the alternate timezone is in effect for the specified time. .sp .LP Local timezone information is used as if \fBmktime()\fR had called \fBtzset()\fR. See \fBctime\fR(3C). .sp .LP The \fBtimegm()\fR function is identical to the \fBmktime()\fR function, except that the \fBtimegm()\fR function ignores both the current time zone and the \fBtm_isdst\fR member and operates as though the time zone were set to UTC. .SH RETURN VALUES .LP If the calendar time can be represented in an object of type \fBtime_t\fR, the \fBmktime()\fR and \fBtimegm()\fR functions return the specified calendar time without changing \fBerrno\fR. If the calendar time cannot be represented, the function returns the value (\fBtime_t\fR)\(mi1 and sets \fBerrno\fR to indicate the error. .SH ERRORS .LP The \fBmktime()\fR and \fBtimegm()\fR functions will fail if: .sp .ne 2 .na \fB\fBEOVERFLOW\fR\fR .ad .RS 13n The date represented by the input \fBtm\fR struct cannot be represented in a \fBtime_t\fR. Note that the \fBerrno\fR setting may change if future revisions to the standards specify a different value. .RE .SH USAGE .LP The \fBmktime()\fR and \fBtimegm()\fR functions are MT-Safe in multithreaded applications, as long as no user-defined function directly modifies one of the following variables: \fBtimezone\fR, \fBaltzone\fR, \fBdaylight\fR, and \fBtzname\fR. See \fBctime\fR(3C). .sp .LP Note that \(mi1 can be a valid return value for the time that is one second before the Epoch. The user should clear \fBerrno\fR before calling \fBmktime()\fR and \fBtimegm()\fR. If \fBmktime()\fR or \fBtimegm()\fR then returns \(mi1, the user should check \fBerrno\fR to determine whether or not an error actually occurred. .sp .LP The \fBmktime()\fR and \fBtimegm()\fR functions assume Gregorian dates. Times before the adoption of the Gregorian calendar will not match historial records. .SH EXAMPLES .LP \fBExample 1 \fRSample code using \fBmktime()\fR. .sp .LP What day of the week is July 4, 2001? .sp .in +2 .nf #include #include static char *const wday[\|] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday", "-unknown-" }; struct tm time_str; /*\|.\|.\|.*/ time_str.tm_year = 2001 - 1900; time_str.tm_mon = 7 - 1; time_str.tm_mday = 4; time_str.tm_hour = 0; time_str.tm_min = 0; time_str.tm_sec = 1; time_str.tm_isdst = \(mi1; if (mktime(&time_str)== \(mi1) time_str.tm_wday=7; printf("%s\en", wday[time_str.tm_wday]); .fi .in -2 .SH BUGS .LP The \fBzoneinfo\fR timezone data files do not transition past Tue Jan 19 03:14:07 2038 UTC. Therefore for 64-bit applications using \fBzoneinfo\fR timezones, calculations beyond this date may not use the correct offset from standard time, and could return incorrect values. This affects the 64-bit versions of \fBmktime()\fR and \fBtimegm()\fR. .SH ATTRIBUTES .LP See \fBattributes\fR(5) for descriptions of the following attributes: .sp .sp .TS box; c | c l | l . ATTRIBUTE TYPE ATTRIBUTE VALUE _ Interface Stability Standard _ MT-Level MT-Safe with exceptions .TE .SH SEE ALSO .LP \fBctime\fR(3C), \fBgetenv\fR(3C), \fBTIMEZONE\fR(4), \fBattributes\fR(5), \fBstandards\fR(5)