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CTIME(3P)		   POSIX Programmer's Manual		     CTIME(3P)

       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.

       ctime, ctime_r — convert a time value to a date and time string

       #include <time.h>

       char *ctime(const time_t *clock);
       char *ctime_r(const time_t *clock, char *buf);

       For ctime(): 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 ctime() function shall convert the time pointed to by clock, repre‐
       senting time in seconds since the Epoch, to local time in the form of a
       string. It shall be equivalent to:


       The  asctime(),	ctime(),  gmtime(),  and  localtime()  functions shall
       return values in one of two static objects: a broken-down  time	struc‐
       ture and an array of char.  Execution of any of the functions may over‐
       write the information returned in either of these objects by any of the
       other functions.

       The ctime() function need not be thread-safe.

       The  ctime_r()  function	 shall convert the calendar time pointed to by
       clock to local time in exactly the same form as	ctime()	 and  put  the
       string  into  the  array	 pointed to by buf (which shall be at least 26
       bytes in size) and return buf.

       Unlike ctime(), the ctime_r() function is not required to  set  tzname.
       If  ctime_r()  does not set tzname, it shall not set daylight and shall
       not set timezone.

       The ctime() function shall return the  pointer  returned	 by  asctime()
       with that broken-down time as an argument.

       Upon  successful	 completion,  ctime_r()	 shall return a pointer to the
       string pointed to by buf.  When an error is encountered, a null pointer
       shall be returned.

       No errors are defined.

       The following sections are informative.


       These  functions	 are included only for compatibility with older imple‐
       mentations. They have undefined behavior if the resulting string	 would
       be  too	long, so the use of these functions should be discouraged.  On
       implementations that do not detect output string length overflow, it is
       possible	 to  overflow  the  output  buffers  in such a way as to cause
       applications to fail, or possible  system  security  violations.	 Also,
       these  functions	 do  not  support  localized date and time formats. To
       avoid these problems, applications should use  strftime()  to  generate
       strings from broken-down times.

       Values  for  the	 broken-down time structure can be obtained by calling
       gmtime() or localtime().

       The ctime_r() function is thread-safe and  shall	 return	 values	 in  a
       user-supplied  buffer instead of possibly using a static data area that
       may be overwritten by each call.

       Attempts to use ctime() or ctime_r() for times before the Epoch or  for
       times  beyond  the  year	 9999 produce undefined results. Refer to asc‐

       The standard developers decided to mark the ctime() and ctime_r() func‐
       tions obsolescent even though they are in the ISO C standard due to the
       possibility of buffer overflow. The ISO C standard  also	 provides  the
       strftime() function which can be used to avoid these problems.

       These functions may be removed in a future version.

       asctime(),  clock(), difftime(), gmtime(), localtime(), mktime(), strf‐
       time(), strptime(), time(), utime()

       The Base Definitions volume of POSIX.1‐2008, <time.h>

       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 Electri‐
       cal 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 https://www.ker‐
       nel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2013			     CTIME(3P)

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