1LOCALTIME(3P) POSIX Programmer's Manual LOCALTIME(3P)
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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
13 localtime, localtime_r — convert a time value to a broken-down local
14 time
15
17 #include <time.h>
18 struct tm *localtime(const time_t *timer);
20 struct tm *localtime_r(const time_t *restrict timer,
21 struct tm *restrict result);
22
24 For localtime(): The functionality described on this reference page is
25 aligned with the ISO C standard. Any conflict between the requirements
26 described here and the ISO C standard is unintentional. This volume of
27 POSIX.1‐2008 defers to the ISO C standard.
28 The localtime() function shall convert the time in seconds since the
30 Epoch pointed to by timer into a broken-down time, expressed as a local
31 time. The function corrects for the timezone and any seasonal time
32 adjustments. Local timezone information is used as though localtime()
33 calls tzset().
34 The relationship between a time in seconds since the Epoch used as an
36 argument to localtime() and the tm structure (defined in the <time.h>
37 header) is that the result shall be as specified in the expression
38 given in the definition of seconds since the Epoch (see the Base Defi‐
39 nitions volume of POSIX.1‐2008, Section 4.15, Seconds Since the Epoch)
40 corrected for timezone and any seasonal time adjustments, where the
41 names in the structure and in the expression correspond.
42 The same relationship shall apply for localtime_r().
44 The localtime() function need not be thread-safe.
46 The asctime(), ctime(), gmtime(), and localtime() functions shall
48 return values in one of two static objects: a broken-down time struc‐
49 ture and an array of type char. Execution of any of the functions may
50 overwrite the information returned in either of these objects by any of
51 the other functions.
52 The localtime_r() function shall convert the time in seconds since the
54 Epoch pointed to by timer into a broken-down time stored in the struc‐
55 ture to which result points. The localtime_r() function shall also
56 return a pointer to that same structure.
57 Unlike localtime(), the localtime_r() function is not required to set
59 tzname. If localtime_r() does not set tzname, it shall not set day‐
60 light and shall not set timezone.
61
63 Upon successful completion, the localtime() function shall return a
64 pointer to the broken-down time structure. If an error is detected,
65 localtime() shall return a null pointer and set errno to indicate the
66 error.
67 Upon successful completion, localtime_r() shall return a pointer to the
69 structure pointed to by the argument result. If an error is detected,
70 localtime_r() shall return a null pointer and set errno to indicate the
71 error.
72
74 The localtime() and localtime_r() functions shall fail if:
75 EOVERFLOW
77 The result cannot be represented.
78 The following sections are informative.
80
82 Getting the Local Date and Time
83 The following example uses the time() function to calculate the time
84 elapsed, in seconds, since January 1, 1970 0:00 UTC (the Epoch), local‐
85 time() to convert that value to a broken-down time, and asctime() to
86 convert the broken-down time values into a printable string.
87 #include <stdio.h>
89 #include <time.h>
90 int main(void)
92 {
93 time_t result;
94 result = time(NULL);
96 printf("%s%ju secs since the Epoch\n",
97 asctime(localtime(&result)),
98 (uintmax_t)result);
99 return(0);
100 }
101 This example writes the current time to stdout in a form like this:
103 Wed Jun 26 10:32:15 1996
105 835810335 secs since the Epoch
106 Getting the Modification Time for a File
108 The following example prints the last data modification timestamp in
109 the local timezone for a given file.
110 #include <stdio.h>
112 #include <time.h>
113 #include <sys/stat.h>
114 int
116 print_file_time(const char *pathname)
117 {
118 struct stat statbuf;
119 struct tm *tm;
120 char timestr[BUFSIZ];
121 if(stat(pathname, &statbuf) == −1)
123 return −1;
124 if((tm = localtime(&statbuf.st_mtime)) == NULL)
125 return −1;
126 if(strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm) == 0)
127 return −1;
128 printf("%s: %s.%09ld\n", pathname, timestr, statbuf.st_mtim.tv_nsec);
129 return 0;
130 }
131 Timing an Event
133 The following example gets the current time, converts it to a string
134 using localtime() and asctime(), and prints it to standard output using
135 fputs(). It then prints the number of minutes to an event being timed.
136 #include <time.h>
138 #include <stdio.h>
139 ...
140 time_t now;
141 int minutes_to_event;
142 ...
143 time(&now);
144 printf("The time is ");
145 fputs(asctime(localtime(&now)), stdout);
146 printf("There are still %d minutes to the event.\n",
147 minutes_to_event);
148 ...
149
151 The localtime_r() function is thread-safe and returns values in a user-
152 supplied buffer instead of possibly using a static data area that may
153 be overwritten by each call.
154
156 None.
157
159 None.
160
162 asctime(), clock(), ctime(), difftime(), getdate(), gmtime(), mktime(),
163 strftime(), strptime(), time(), tzset(), utime()
164 The Base Definitions volume of POSIX.1‐2008, Section 4.15, Seconds
166 Since the Epoch, <time.h>
167
169 Portions of this text are reprinted and reproduced in electronic form
170 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
171 -- Portable Operating System Interface (POSIX), The Open Group Base
172 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
173 cal and Electronics Engineers, Inc and The Open Group. (This is
174 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
175 event of any discrepancy between this version and the original IEEE and
176 The Open Group Standard, the original IEEE and The Open Group Standard
177 is the referee document. The original Standard can be obtained online
178 at http://www.unix.org/online.html .
179 Any typographical or formatting errors that appear in this page are
181 most likely to have been introduced during the conversion of the source
182 files to man page format. To report such errors, see https://www.ker‐
183 nel.org/doc/man-pages/reporting_bugs.html .
184IEEE/The Open Group 2013 LOCALTIME(3P)