1LOCALTIME(3P) POSIX Programmer's Manual LOCALTIME(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 localtime, localtime_r — convert a time value to a broken-down local
13 time
14
16 #include <time.h>
17 struct tm *localtime(const time_t *timer);
19 struct tm *localtime_r(const time_t *restrict timer,
20 struct tm *restrict result);
21
23 For localtime(): The functionality described on this reference page is
24 aligned with the ISO C standard. Any conflict between the requirements
25 described here and the ISO C standard is unintentional. This volume of
26 POSIX.1‐2017 defers to the ISO C standard.
27 The localtime() function shall convert the time in seconds since the
29 Epoch pointed to by timer into a broken-down time, expressed as a local
30 time. The function corrects for the timezone and any seasonal time
31 adjustments. Local timezone information is used as though localtime()
32 calls tzset().
33 The relationship between a time in seconds since the Epoch used as an
35 argument to localtime() and the tm structure (defined in the <time.h>
36 header) is that the result shall be as specified in the expression
37 given in the definition of seconds since the Epoch (see the Base Defi‐
38 nitions volume of POSIX.1‐2017, Section 4.16, Seconds Since the Epoch)
39 corrected for timezone and any seasonal time adjustments, where the
40 names in the structure and in the expression correspond.
41 The same relationship shall apply for localtime_r().
43 The localtime() function need not be thread-safe.
45 The asctime(), ctime(), gmtime(), and localtime() functions shall
47 return values in one of two static objects: a broken-down time struc‐
48 ture and an array of type char. Execution of any of the functions may
49 overwrite the information returned in either of these objects by any of
50 the other functions.
51 The localtime_r() function shall convert the time in seconds since the
53 Epoch pointed to by timer into a broken-down time stored in the struc‐
54 ture to which result points. The localtime_r() function shall also
55 return a pointer to that same structure.
56 Unlike localtime(), the localtime_r() function is not required to set
58 tzname. If localtime_r() sets tzname, it shall also set daylight and
59 timezone. 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>
90 #include <time.h>
91 int main(void)
93 {
94 time_t result;
95 result = time(NULL);
97 printf("%s%ju secs since the Epoch\n",
98 asctime(localtime(&result)),
99 (uintmax_t)result);
100 return(0);
101 }
102 This example writes the current time to stdout in a form like this:
104 Wed Jun 26 10:32:15 1996
107 835810335 secs since the Epoch
108 Getting the Modification Time for a File
110 The following example prints the last data modification timestamp in
111 the local timezone for a given file.
112 #include <stdio.h>
115 #include <time.h>
116 #include <sys/stat.h>
117 int
119 print_file_time(const char *pathname)
120 {
121 struct stat statbuf;
122 struct tm *tm;
123 char timestr[BUFSIZ];
124 if(stat(pathname, &statbuf) == -1)
126 return -1;
127 if((tm = localtime(&statbuf.st_mtime)) == NULL)
128 return -1;
129 if(strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm) == 0)
130 return -1;
131 printf("%s: %s.%09ld\n", pathname, timestr, statbuf.st_mtim.tv_nsec);
132 return 0;
133 }
134 Timing an Event
136 The following example gets the current time, converts it to a string
137 using localtime() and asctime(), and prints it to standard output using
138 fputs(). It then prints the number of minutes to an event being timed.
139 #include <time.h>
142 #include <stdio.h>
143 ...
144 time_t now;
145 int minutes_to_event;
146 ...
147 time(&now);
148 printf("The time is ");
149 fputs(asctime(localtime(&now)), stdout);
150 printf("There are still %d minutes to the event.\n",
151 minutes_to_event);
152 ...
153
155 The localtime_r() function is thread-safe and returns values in a user-
156 supplied buffer instead of possibly using a static data area that may
157 be overwritten by each call.
158
160 None.
161
163 None.
164
166 asctime(), clock(), ctime(), difftime(), getdate(), gmtime(), mktime(),
167 strftime(), strptime(), time(), tzset(), utime()
168 The Base Definitions volume of POSIX.1‐2017, Section 4.16, Seconds
170 Since the Epoch, <time.h>
171
173 Portions of this text are reprinted and reproduced in electronic form
174 from IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
175 table Operating System Interface (POSIX), The Open Group Base Specifi‐
176 cations Issue 7, 2018 Edition, Copyright (C) 2018 by the Institute of
177 Electrical and Electronics Engineers, Inc and The Open Group. In the
178 event of any discrepancy between this version and the original IEEE and
179 The Open Group Standard, the original IEEE and The Open Group Standard
180 is the referee document. The original Standard can be obtained online
181 at http://www.opengroup.org/unix/online.html .
182 Any typographical or formatting errors that appear in this page are
184 most likely to have been introduced during the conversion of the source
185 files to man page format. To report such errors, see https://www.ker‐
186 nel.org/doc/man-pages/reporting_bugs.html .
187IEEE/The Open Group 2017 LOCALTIME(3P)