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localtime_s, _localtime32_s, _localtime64_s

Converts a time_t time value to a tm structure, and corrects for the local time zone. These functions are versions of localtime, _localtime32, _localtime64 with security enhancements as described in Security features in the CRT.


errno_t localtime_s(
   struct tm* const tmDest,
   time_t const* const sourceTime
errno_t _localtime32_s(
   struct tm* tmDest,
   __time32_t const* sourceTime
errno_t _localtime64_s(
   struct tm* tmDest,
   __time64_t const* sourceTime


Pointer to the time structure to be filled in.

Pointer to the stored time.

Return value

Zero if successful. The return value is an error code if there's a failure. Error codes are defined in Errno.h. For a listing of these errors, see errno.

Error conditions

tmDest sourceTime Return value Value in tmDest Invokes invalid parameter handler
NULL any EINVAL Not modified Yes
Not NULL (points to valid memory) NULL EINVAL All fields set to -1 Yes
Not NULL (points to valid memory) less than 0 or greater than _MAX__TIME64_T EINVAL All fields set to -1 No

The first two error conditions invoke the invalid parameter handler, as described in Parameter validation. If execution is allowed to continue, these functions set errno to EINVAL and return EINVAL.


The localtime_s function converts a time stored as a time_t value and stores the result in a structure of type tm. The time_t value sourceTime represents the seconds elapsed since midnight (00:00:00), January 1, 1970, UTC. This value is often obtained from the time function.

localtime_s corrects for the local time zone if the user first sets the global environment variable TZ. When TZ is set, three other environment variables (_timezone, _daylight, and _tzname) are automatically set as well. If the TZ variable isn't set, localtime_s attempts to use the time zone information specified in the Date/Time application in Control Panel. If this information can't be obtained, PST8PDT, which signifies the Pacific time zone, is used by default. See _tzset for a description of these variables. TZ is a Microsoft extension and not part of the ANSI standard definition of localtime.


The target environment should try to determine whether daylight saving time is in effect.

_localtime64_s, which uses the __time64_t structure, allows dates to be expressed up through 23:59:59, January 18, 3001, coordinated universal time (UTC), whereas _localtime32_s represents dates through 23:59:59 January 18, 2038, UTC.

localtime_s is an inline function that evaluates to _localtime64_s, and time_t is equivalent to __time64_t. If you need to force the compiler to interpret time_t as the old 32-bit time_t, you can define _USE_32BIT_TIME_T, which causes localtime_s to evaluate to _localtime32_s. We don't recommend _USE_32BIT_TIME_T, because your application may fail after January 18, 2038, and it isn't allowed on 64-bit platforms.

The fields of the structure type tm store the following values, each of which is an int.

Field Description
tm_sec Seconds after minute (0 - 59).
tm_min Minutes after hour (0 - 59).
tm_hour Hours since midnight (0 - 23).
tm_mday Day of month (1 - 31).
tm_mon Month (0 - 11; January = 0).
tm_year Year (current year minus 1900).
tm_wday Day of week (0 - 6; Sunday = 0).
tm_yday Day of year (0 - 365; January 1 = 0).
tm_isdst Positive value if daylight saving time is in effect; 0 if daylight saving time isn't in effect; negative value if status of daylight saving time is unknown.

If the TZ environment variable is set, the C run-time library assumes rules appropriate to the United States for implementing the calculation of daylight saving time (DST).

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.


Routine Required C header Required C++ header
localtime_s, _localtime32_s, _localtime64_s <time.h> <ctime> or <time.h>

For more compatibility information, see Compatibility.


// crt_localtime_s.c
// This program uses _time64 to get the current time
// and then uses _localtime64_s() to convert this time to a structure
// representing the local time. The program converts the result
// from a 24-hour clock to a 12-hour clock and determines the
// proper extension (AM or PM).

#include <stdio.h>
#include <string.h>
#include <time.h>

int main( void )
    struct tm newtime;
    char am_pm[] = "AM";
    __time64_t long_time;
    char timebuf[26];
    errno_t err;

    // Get time as 64-bit integer.
    _time64( &long_time );
    // Convert to local time.
    err = _localtime64_s( &newtime, &long_time );
    if (err)
        printf("Invalid argument to _localtime64_s.");
    if( newtime.tm_hour > 12 )        // Set up extension.
        strcpy_s( am_pm, sizeof(am_pm), "PM" );
    if( newtime.tm_hour > 12 )        // Convert from 24-hour
        newtime.tm_hour -= 12;        // to 12-hour clock.
    if( newtime.tm_hour == 0 )        // Set hour to 12 if midnight.
        newtime.tm_hour = 12;

    // Convert to an ASCII representation.
    err = asctime_s(timebuf, 26, &newtime);
    if (err)
        printf("Invalid argument to asctime_s.");
    printf( "%.19s %s\n", timebuf, am_pm );
Fri Apr 25 01:19:27 PM

See also

Time management
asctime_s, _wasctime_s
ctime, _ctime32, _ctime64, _wctime, _wctime32, _wctime64
_ftime, _ftime32, _ftime64
gmtime_s, _gmtime32_s, _gmtime64_s
localtime, _localtime32, _localtime64
time, _time32, _time64