PROLOG

       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.

NAME

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

SYNOPSIS

       #include <time.h>

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

DESCRIPTION

       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, representing time in
       seconds since the Epoch, to local time in the form of a string. It shall be equivalent to:

           asctime(localtime(clock))

       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 char.  Execution of any
       of the functions may overwrite 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.

RETURN VALUE

       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.

ERRORS

       No errors are defined.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       These functions are included only for compatibility with older implementations. 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 asctime().

RATIONALE

       The  standard  developers  decided to mark the ctime() and ctime_r() functions 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.

FUTURE DIRECTIONS

       These functions may be removed in a future version.

SEE ALSO

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

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

COPYRIGHT

       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 https://www.kernel.org/doc/man-pages/reporting_bugs.html .