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 .