LOCALTIME(P) POSIX Programmer's Manual LOCALTIME(P)
localtime, localtime_r - convert a time value to a broken-down local time
struct tm *localtime(const time_t *timer);
struct tm *localtime_r(const time_t *restrict timer,
struct tm *restrict result);
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 stan-
dard is unintentional. This volume of IEEE Std 1003.1-2001 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 local-
time() 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 IEEE Std 1003.1-2001, Section 4.14, Seconds Since the Epoch)
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 reentrant. A function that is not required to be
reentrant is not required to 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 local-
time_r() function shall also return a pointer to that same structure.
Unlike localtime(), the reentrant version is not required to set tzname.
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 error.
Upon successful completion, localtime_r() shall return a pointer to the structure pointed
to by the argument result.
The localtime() function shall fail if:
The result cannot be represented.
The following sections are informative.
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 string.
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 1996
835810335 secs since the Epoch
Getting the Modification Time for a File
The following example gets the modification time for a file. The localtime() function con-
verts the time_t value of the last modification date, obtained by a previous call to
stat(), into a tm structure that contains the year, month, day, and so on.
struct stat statbuf;
tm = localtime(&statbuf.st_mtime);
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 being timed.
printf("The time is ");
printf("There are still %d minutes to the event.\n",
The localtime_r() function is thread-safe and returns values in a user-supplied buffer
instead of possibly using a static data area that may be overwritten by each call.
asctime() , clock() , ctime() , difftime() , getdate() , gmtime() , mktime() , strftime()
, strptime() , time() , utime() , the Base Definitions volume of IEEE Std 1003.1-2001,
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by
the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 LOCALTIME(P)