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CTIME(3P)                  POSIX Programmer's Manual                 CTIME(3P)
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, repre-
       senting 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  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.
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 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-
       time().
RATIONALE
       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.
FUTURE DIRECTIONS
       These functions may be removed in a future version.
SEE ALSO
       asctime(),  clock(), difftime(), gmtime(), localtime(), mktime(), strf-
       time(), 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 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)