1MKTIME(3P) POSIX Programmer's Manual MKTIME(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
12 mktime — convert broken-down time into time since the Epoch
13
15 #include <time.h>
16 time_t mktime(struct tm *timeptr);
18
20 The functionality described on this reference page is aligned with the
21 ISO C standard. Any conflict between the requirements described here
22 and the ISO C standard is unintentional. This volume of POSIX.1‐2017
23 defers to the ISO C standard.
24 The mktime() function shall convert the broken-down time, expressed as
26 local time, in the structure pointed to by timeptr, into a time since
27 the Epoch value with the same encoding as that of the values returned
28 by time(). The original values of the tm_wday and tm_yday components
29 of the structure shall be ignored, and the original values of the other
30 components shall not be restricted to the ranges described in <time.h>.
31 A positive or 0 value for tm_isdst shall cause mktime() to presume ini‐
33 tially that Daylight Savings Time, respectively, is or is not in effect
34 for the specified time. A negative value for tm_isdst shall cause
35 mktime() to attempt to determine whether Daylight Savings Time is in
36 effect for the specified time.
37 Local timezone information shall be set as though mktime() called
39 tzset().
40 The relationship between the tm structure (defined in the <time.h>
42 header) and the time in seconds since the Epoch is that the result
43 shall be as specified in the expression given in the definition of sec‐
44 onds since the Epoch (see the Base Definitions volume of POSIX.1‐2017,
45 Section 4.16, Seconds Since the Epoch) corrected for timezone and any
46 seasonal time adjustments, where the names other than tm_yday in the
47 structure and in the expression correspond, and the tm_yday value used
48 in the expression is the day of the year from 0 to 365 inclusive, cal‐
49 culated from the other tm structure members specified in <time.h>
50 (excluding tm_wday).
51 Upon successful completion, the values of the tm_wday and tm_yday com‐
53 ponents of the structure shall be set appropriately, and the other com‐
54 ponents shall be set to represent the specified time since the Epoch,
55 but with their values forced to the ranges indicated in the <time.h>
56 entry; the final value of tm_mday shall not be set until tm_mon and
57 tm_year are determined.
58
60 The mktime() function shall return the specified time since the Epoch
61 encoded as a value of type time_t. If the time since the Epoch cannot
62 be represented, the function shall return the value (time_t)-1 and set
63 errno to indicate the error.
64
66 The mktime() function shall fail if:
67 EOVERFLOW
69 The result cannot be represented.
70 The following sections are informative.
72
74 What day of the week is July 4, 2001?
75 #include <stdio.h>
78 #include <time.h>
79 struct tm time_str;
81 char daybuf[20];
83 int main(void)
85 {
86 time_str.tm_year = 2001 — 1900;
87 time_str.tm_mon = 7 — 1;
88 time_str.tm_mday = 4;
89 time_str.tm_hour = 0;
90 time_str.tm_min = 0;
91 time_str.tm_sec = 1;
92 time_str.tm_isdst = -1;
93 if (mktime(&time_str) == -1)
94 (void)puts("-unknown-");
95 else {
96 (void)strftime(daybuf, sizeof(daybuf), "%A", &time_str);
97 (void)puts(daybuf);
98 }
99 return 0;
100 }
101
103 None.
104
106 None.
107
109 None.
110
112 asctime(), clock(), ctime(), difftime(), gmtime(), localtime(), strf‐
113 time(), strptime(), time(), tzset(), utime()
114 The Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds
116 Since the Epoch, <time.h>
117
119 Portions of this text are reprinted and reproduced in electronic form
120 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
121 table Operating System Interface (POSIX), The Open Group Base Specifi‐
122 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
123 Electrical and Electronics Engineers, Inc and The Open Group. In the
124 event of any discrepancy between this version and the original IEEE and
125 The Open Group Standard, the original IEEE and The Open Group Standard
126 is the referee document. The original Standard can be obtained online
127 at http://www.opengroup.org/unix/online.html .
128 Any typographical or formatting errors that appear in this page are
130 most likely to have been introduced during the conversion of the source
131 files to man page format. To report such errors, see https://www.ker‐
132 nel.org/doc/man-pages/reporting_bugs.html .
133IEEE/The Open Group 2017 MKTIME(3P)