1mktime(3C) Standard C Library Functions mktime(3C)
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6 mktime - converts a tm structure to a calendar time
7
9 #include <time.h>
10 time_t mktime(struct tm *timeptr);
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15 The mktime() function converts the time represented by the tm structure
16 pointed to by timeptr into a calendar time (the number of seconds
17 since 00:00:00 UTC, January 1, 1970).
18 The tm structure contains the following members:
21 int tm_sec; /* seconds after the minute [0, 60] */
23 int tm_min; /* minutes after the hour [0, 59] */
24 int tm_hour; /* hour since midnight [0, 23] */
25 int tm_mday; /* day of the month [1, 31] */
26 int tm_mon; /* months since January [0, 11] */
27 int tm_year; /* years since 1900 */
28 int tm_wday; /* days since Sunday [0, 6] */
29 int tm_yday; /* days since January 1 [0, 365] */
30 int tm_isdst; /* flag for daylight savings time */
31 In addition to computing the calendar time, mktime() normalizes the
35 supplied tm structure. The original values of the tm_wday and tm_yday
36 components of the structure are ignored, and the original values of the
37 other components are not restricted to the ranges indicated in the def‐
38 inition of the structure. On successful completion, the values of the
39 tm_wday and tm_yday components are set appropriately, and the other
40 components are set to represent the specified calendar time, but with
41 their values forced to be within the appropriate ranges. The final
42 value of tm_mday is not set until tm_mon and tm_year are determined.
43 The tm_year member must be for year 1901 or later. Calendar times
46 before 20:45:52 UTC, December 13, 1901 or after 03:14:07 UTC, January
47 19, 2038 cannot be represented. Portable applications should not try to
48 create dates before 00:00:00 UTC, January 1, 1970 or after 00:00:00
49 UTC, January 1, 2038.
50 The original values of the components may be either greater than or
53 less than the specified range. For example, a tm_hour of −1 means 1
54 hour before midnight, tm_mday of 0 means the day preceding the current
55 month, and tm_mon of −2 means 2 months before January of tm_year.
56 If tm_isdst is positive, the original values are assumed to be in the
59 alternate timezone. If it turns out that the alternate timezone is not
60 valid for the computed calendar time, then the components are adjusted
61 to the main timezone. Likewise, if tm_isdst is zero, the original val‐
62 ues are assumed to be in the main timezone and are converted to the
63 alternate timezone if the main timezone is not valid. If tm_isdst is
64 negative, mktime() attempts to determine whether the alternate timezone
65 is in effect for the specified time.
66 Local timezone information is used as if mktime() had called tzset().
69 See ctime(3C).
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72 If the calendar time can be represented in an object of type time_t,
73 mktime() returns the specified calendar time without changing errno. If
74 the calendar time cannot be represented, the function returns the value
75 (time_t)−1 and sets errno to indicate the error.
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78 The mktime() function will fail if:
79 EOVERFLOW The date represented by the input tm struct cannot be rep‐
81 resented in a time_t. Note that the errno setting may
82 change if future revisions to the standards specify a dif‐
83 ferent value.
84
87 The mktime() function is MT-Safe in multithreaded applications, as
88 long as no user-defined function directly modifies one of the following
89 variables: timezone, altzone, daylight, and tzname. See ctime(3C).
90 Note that −1 can be a valid return value for the time that is one sec‐
93 ond before the Epoch. The user should clear errno before calling
94 mktime(). If mktime() then returns −1, the user should check errno to
95 determine whether or not an error actually occurred.
96 The mktime() function assumes Gregorian dates. Times before the adop‐
99 tion of the Gregorian calendar will not match historial records.
100
102 Example 1 Sample code using mktime().
103 What day of the week is July 4, 2001?
106 #include <stdio.h>
109 #include <time.h>
110 static char *const wday[] = {
111 "Sunday", "Monday", "Tuesday", "Wednesday",
112 "Thursday", "Friday", "Saturday", "-unknown-"
113 };
114 struct tm time_str;
115 /*...*/
116 time_str.tm_year = 2001 - 1900;
117 time_str.tm_mon = 7 - 1;
118 time_str.tm_mday = 4;
119 time_str.tm_hour = 0;
120 time_str.tm_min = 0;
121 time_str.tm_sec = 1;
122 time_str.tm_isdst = −1;
123 if (mktime(&time_str)== −1)
124 time_str.tm_wday=7;
125 printf("%s\n", wday[time_str.tm_wday]);
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129 The zoneinfo timezone data files do not transition past Tue Jan 19
130 03:14:07 2038 UTC. Therefore for 64-bit applications using zoneinfo
131 timezones, calculations beyond this date may not use the correct offset
132 from standard time, and could return incorrect values. This affects the
133 64-bit version of mktime().
134
136 See attributes(5) for descriptions of the following attributes:
137 ┌─────────────────────────────┬─────────────────────────────┐
142 │ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
143 ├─────────────────────────────┼─────────────────────────────┤
144 │Interface Stability │Standard │
145 ├─────────────────────────────┼─────────────────────────────┤
146 │MT-Level │MT-Safe with exceptions │
147 └─────────────────────────────┴─────────────────────────────┘
148
150 ctime(3C), getenv(3C), TIMEZONE(4), attributes(5), standards(5)
151SunOS 5.11 1 Nov 2003 mktime(3C)