This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
For localtime(): The functionality described on this reference page
is aligned with the ISO C standard. Any conflict between the
requirements described here and the ISO C standard is unintentional.
This volume of POSIX.1‐2008 defers to the ISO C standard.
The localtime() function shall convert the time in seconds since the
Epoch pointed to by timer into a broken-down time, expressed as a
local time. The function corrects for the timezone and any seasonal
time adjustments. Local timezone information is used as though
localtime() calls tzset().
The relationship between a time in seconds since the Epoch used as an
argument to localtime() and the tm structure (defined in the <time.h>
header) is that the result shall be as specified in the expression
given in the definition of seconds since the Epoch (see the Base
Definitions volume of POSIX.1‐2008, Section 4.15, Seconds Since theEpoch) corrected for timezone and any seasonal time adjustments,
where the names in the structure and in the expression correspond.
The same relationship shall apply for localtime_r().
The localtime() function need not be thread-safe.
The asctime(), ctime(), gmtime(), and localtime() functions shall
return values in one of two static objects: a broken-down time
structure and an array of type char. Execution of any of the
functions may overwrite the information returned in either of these
objects by any of the other functions.
The localtime_r() function shall convert the time in seconds since
the Epoch pointed to by timer into a broken-down time stored in the
structure to which result points. The localtime_r() function shall
also return a pointer to that same structure.
Unlike localtime(), the localtime_r() function is not required to set
tzname. If localtime_r() does not set tzname, it shall not set
daylight and shall not set timezone.
Upon successful completion, the localtime() function shall return a
pointer to the broken-down time structure. If an error is detected,
localtime() shall return a null pointer and set errno to indicate the
Upon successful completion, localtime_r() shall return a pointer to
the structure pointed to by the argument result. If an error is
detected, localtime_r() shall return a null pointer and set errno to
indicate the error.
Getting the Local Date and Time
The following example uses the time() function to calculate the time
elapsed, in seconds, since January 1, 1970 0:00 UTC (the Epoch),
localtime() to convert that value to a broken-down time, and
asctime() to convert the broken-down time values into a printable
#include <stdio.h>#include <time.h>
result = time(NULL);
printf("%s%ju secs since the Epoch\n",
This example writes the current time to stdout in a form like this:
Wed Jun 26 10:32:15 1996835810335 secs since the EpochGetting the Modification Time for a File
The following example prints the last data modification timestamp in
the local timezone for a given file.
#include <stdio.h>#include <time.h>#include <sys/stat.h>
print_file_time(const char *pathname)
struct stat statbuf;
struct tm *tm;
if(stat(pathname, &statbuf) == −1)
if((tm = localtime(&statbuf.st_mtime)) == NULL)
if(strftime(timestr, sizeof(timestr), "%Y-%m-%d %H:%M:%S", tm) == 0)
printf("%s: %s.%09ld\n", pathname, timestr, statbuf.st_mtim.tv_nsec);
Timing an Event
The following example gets the current time, converts it to a string
using localtime() and asctime(), and prints it to standard output
using fputs(). It then prints the number of minutes to an event
#include <time.h>#include <stdio.h>...time_t now;int minutes_to_event;...time(&now);printf("The time is ");fputs(asctime(localtime(&now)), stdout);printf("There are still %d minutes to the event.\n",minutes_to_event);...
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
IEEE/The Open Group 2013 LOCALTIME(3P)