1LOCALTIME(P) POSIX Programmer's Manual LOCALTIME(P)
2
6 localtime, localtime_r - convert a time value to a broken-down local
7 time
8
10 #include <time.h>
11 struct tm *localtime(const time_t *timer);
13 struct tm *localtime_r(const time_t *restrict timer,
16 struct tm *restrict result);
17
20 For localtime(): The functionality described on this reference page
21 is aligned with the ISO C standard. Any conflict between the require‐
22 ments described here and the ISO C standard is unintentional. This vol‐
23 ume of IEEE Std 1003.1-2001 defers to the ISO C standard.
24 The localtime() function shall convert the time in seconds since the
26 Epoch pointed to by timer into a broken-down time, expressed as a local
27 time. The function corrects for the timezone and any seasonal time
28 adjustments. Local timezone information is used as though local‐
29 time() calls tzset().
30 The relationship between a time in seconds since the Epoch used as an
32 argument to localtime() and the tm structure (defined in the <time.h>
33 header) is that the result shall be as specified in the expression
34 given in the definition of seconds since the Epoch (see the Base Defi‐
35 nitions volume of IEEE Std 1003.1-2001, Section 4.14, Seconds Since the
36 Epoch) corrected for timezone and any seasonal time adjustments, where
37 the names in the structure and in the expression correspond.
38 The same relationship shall apply for localtime_r().
40 The localtime() function need not be reentrant. A function that is not
42 required to be reentrant is not required to be thread-safe.
43 The asctime(), ctime(), gmtime(), and localtime() functions shall
45 return values in one of two static objects: a broken-down time struc‐
46 ture and an array of type char. Execution of any of the functions may
47 overwrite the information returned in either of these objects by any of
48 the other functions.
49 The localtime_r() function shall convert the time in seconds since the
51 Epoch pointed to by timer into a broken-down time stored in the struc‐
52 ture to which result points. The localtime_r() function shall also
53 return a pointer to that same structure.
54 Unlike localtime(), the reentrant version is not required to set
56 tzname.
57
59 Upon successful completion, the localtime() function shall return a
60 pointer to the broken-down time structure. If an error is detected,
61 localtime() shall return a null pointer and set errno to indicate the
62 error.
63 Upon successful completion, localtime_r() shall return a pointer to the
65 structure pointed to by the argument result.
66
68 The localtime() function shall fail if:
69 EOVERFLOW
71 The result cannot be represented.
72 The following sections are informative.
75
77 Getting the Local Date and Time
78 The following example uses the time() function to calculate the time
79 elapsed, in seconds, since January 1, 1970 0:00 UTC (the Epoch), local‐
80 time() to convert that value to a broken-down time, and asctime() to
81 convert the broken-down time values into a printable string.
82 #include <stdio.h>
85 #include <time.h>
86 int main(void)
89 {
90 time_t result;
91 result = time(NULL);
94 printf("%s%ju secs since the Epoch\n",
95 asctime(localtime(&result)),
96 (uintmax_t)result);
97 return(0);
98 }
99 This example writes the current time to stdout in a form like this:
101 Wed Jun 26 10:32:15 1996
104 835810335 secs since the Epoch
105 Getting the Modification Time for a File
107 The following example gets the modification time for a file. The local‐
108 time() function converts the time_t value of the last modification
109 date, obtained by a previous call to stat(), into a tm structure that
110 contains the year, month, day, and so on.
111 #include <time.h>
114 ...
115 struct stat statbuf;
116 ...
117 tm = localtime(&statbuf.st_mtime);
118 ...
119 Timing an Event
121 The following example gets the current time, converts it to a string
122 using localtime() and asctime(), and prints it to standard output using
123 fputs(). It then prints the number of minutes to an event being timed.
124 #include <time.h>
127 #include <stdio.h>
128 ...
129 time_t now;
130 int minutes_to_event;
131 ...
132 time(&now);
133 printf("The time is ");
134 fputs(asctime(localtime(&now)), stdout);
135 printf("There are still %d minutes to the event.\n",
136 minutes_to_event);
137 ...
138
140 The localtime_r() function is thread-safe and returns values in a user-
141 supplied buffer instead of possibly using a static data area that may
142 be overwritten by each call.
143
145 None.
146
148 None.
149
151 asctime() , clock() , ctime() , difftime() , getdate() , gmtime() ,
152 mktime() , strftime() , strptime() , time() , utime() , the Base Defi‐
153 nitions volume of IEEE Std 1003.1-2001, <time.h>
154
156 Portions of this text are reprinted and reproduced in electronic form
157 from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
158 -- Portable Operating System Interface (POSIX), The Open Group Base
159 Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
160 Electrical and Electronics Engineers, Inc and The Open Group. In the
161 event of any discrepancy between this version and the original IEEE and
162 The Open Group Standard, the original IEEE and The Open Group Standard
163 is the referee document. The original Standard can be obtained online
164 at http://www.opengroup.org/unix/online.html .
165IEEE/The Open Group 2003 LOCALTIME(P)