TIME(3)                    POSIX Programmer's Manual                   TIME(3)



PPRROOLLOOGG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

NNAAMMEE
       time -- get time

SSYYNNOOPPSSIISS
       #include <time.h>

       time_t time(time_t *_t_l_o_c);

DDEESSCCRRIIPPTTIIOONN
       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.1-2017
       defers to the ISO C standard.

       The _t_i_m_e() function shall return the value of time in seconds since the
       Epoch.

       The _t_l_o_c argument points to an area where the return value is also
       stored. If _t_l_o_c is a null pointer, no value is stored.

RREETTUURRNN VVAALLUUEE
       Upon successful completion, _t_i_m_e() shall return the value of time.
       Otherwise, (ttiimmee__tt)-1 shall be returned.

EERRRROORRSS
       The _t_i_m_e() function may fail if:

       EEOOVVEERRFFLLOOWW
              The number of seconds since the Epoch will not fit in an object
              of type ttiimmee__tt.

       _T_h_e _f_o_l_l_o_w_i_n_g _s_e_c_t_i_o_n_s _a_r_e _i_n_f_o_r_m_a_t_i_v_e_.

EEXXAAMMPPLLEESS
   GGeettttiinngg tthhee CCuurrrreenntt TTiimmee
       The following example uses the _t_i_m_e() function to calculate the time
       elapsed, in seconds, since the Epoch, _l_o_c_a_l_t_i_m_e() to convert that value
       to a broken-down time, and _a_s_c_t_i_m_e() to convert the broken-down time
       values into a printable string.


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

           int main(void)
           {
           time_t result;

               result = time(NULL);
               printf("%s%ju secs since the Epoch\n",
                   asctime(localtime(&result)),
                       (uintmax_t)result);
               return(0);
           }

       This example writes the current time to _s_t_d_o_u_t in a form like this:


           Wed Jun 26 10:32:15 1996
           835810335 secs since the Epoch

   TTiimmiinngg aann EEvveenntt
       The following example gets the current time, prints it out in the
       user's format, and prints the number of minutes to an event being
       timed.


           #include <time.h>
           #include <stdio.h>
           ...
           time_t now;
           int minutes_to_event;
           ...
           time(&now);
           minutes_to_event = ...;
           printf("The time is ");
           puts(asctime(localtime(&now)));
           printf("There are %d minutes to the event.\n",
               minutes_to_event);
           ...

AAPPPPLLIICCAATTIIOONN UUSSAAGGEE
       None.

RRAATTIIOONNAALLEE
       The _t_i_m_e() function returns a value in seconds while _c_l_o_c_k___g_e_t_t_i_m_e()
       and _g_e_t_t_i_m_e_o_f_d_a_y() return a ssttrruucctt ttiimmeessppeecc (seconds and nanoseconds)
       and ssttrruucctt ttiimmeevvaall (seconds and microseconds), respectively, and are
       therefore capable of returning more precise times. The _t_i_m_e_s() function
       is also capable of more precision than _t_i_m_e() as it returns a value in
       clock ticks, although it returns the elapsed time since an arbitrary
       point such as system boot time, not since the epoch.

       Implementations in which ttiimmee__tt is a 32-bit signed integer (many
       historical implementations) fail in the year 2038. POSIX.1-2008 does
       not address this problem. However, the use of the ttiimmee__tt type is
       mandated in order to ease the eventual fix.

       On some systems the _t_i_m_e() function is implemented using a system call
       that does not return an error condition in addition to the return
       value. On these systems it is impossible to differentiate between valid
       and invalid return values and hence overflow conditions cannot be
       reliably detected.

       The use of the _<_t_i_m_e_._h_> header instead of _<_s_y_s_/_t_y_p_e_s_._h_> allows
       compatibility with the ISO C standard.

       Many historical implementations (including Version 7) and the 1984
       /usr/group standard use lloonngg instead of ttiimmee__tt.  This volume of
       POSIX.1-2017 uses the latter type in order to agree with the ISO C
       standard.

FFUUTTUURREE DDIIRREECCTTIIOONNSS
       In a future version of this volume of POSIX.1-2017, ttiimmee__tt is likely to
       be required to be capable of representing times far in the future.
       Whether this will be mandated as a 64-bit type or a requirement that a
       specific date in the future be representable (for example, 10000 AD) is
       not yet determined. Systems purchased after the approval of this volume
       of POSIX.1-2017 should be evaluated to determine whether their lifetime
       will extend past 2038.

SSEEEE AALLSSOO
       _a_s_c_t_i_m_e(), _c_l_o_c_k(), _c_l_o_c_k___g_e_t_r_e_s(), _c_t_i_m_e(), _d_i_f_f_t_i_m_e(), _f_u_t_i_m_e_n_s(),
       _g_e_t_t_i_m_e_o_f_d_a_y(), _g_m_t_i_m_e(), _l_o_c_a_l_t_i_m_e(), _m_k_t_i_m_e(), _s_t_r_f_t_i_m_e(),
       _s_t_r_p_t_i_m_e(), _t_i_m_e_s(), _u_t_i_m_e()

       The Base Definitions volume of POSIX.1-2017, <<ttiimmee..hh>>

CCOOPPYYRRIIGGHHTT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 original Standard can
       be obtained online at http://www.opengroup.org/unix/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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                              TIME(3)
