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ASCTIME(3P)                POSIX Programmer's Manual               ASCTIME(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
       asctime, asctime_r -- convert date and time to a string
SYNOPSIS
       #include <time.h>
       char *asctime(const struct tm *timeptr);
       char *asctime_r(const struct tm *restrict tm, char *restrict buf);
DESCRIPTION
       For asctime(): 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 asctime() function shall convert the broken-down time in the struc-
       ture pointed to by timeptr into a string in the form:
           Sun Sep 16 01:03:52 1973\n\0
       using the equivalent of the following algorithm:
           char *asctime(const struct tm *timeptr)
           {
               static char wday_name[7][3] = {
                   "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
               };
               static char mon_name[12][3] = {
                   "Jan", "Feb", "Mar", "Apr", "May", "Jun",
                   "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
               };
               static char result[26];
               sprintf(result, "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n",
                   wday_name[timeptr->tm_wday],
                   mon_name[timeptr->tm_mon],
                   timeptr->tm_mday, timeptr->tm_hour,
                   timeptr->tm_min, timeptr->tm_sec,
                   1900 + timeptr->tm_year);
               return result;
           }
       However,   the   behavior   is   undefined   if   timeptr->tm_wday   or
       timeptr->tm_mon  are  not  within  the  normal  ranges  as  defined  in
       <time.h>, or if timeptr->tm_year  exceeds  {INT_MAX}-1990,  or  if  the
       above  algorithm would attempt to generate more than 26 bytes of output
       (including the terminating null).
       The tm structure is defined in the <time.h> header.
       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 type char.  Execution of any of the functions  may
       overwrite the information returned in either of these objects by any of
       the other functions.
       The asctime() function need not be thread-safe.
       The asctime_r() function shall convert  the  broken-down  time  in  the
       structure  pointed  to  by  tm  into a string (of the same form as that
       returned by asctime(), and with the same undefined behavior when  input
       or  output  is out of range) that is placed in the user-supplied buffer
       pointed to by buf (which shall contain at  least  26  bytes)  and  then
       return buf.
RETURN VALUE
       Upon  successful  completion,  asctime()  shall return a pointer to the
       string.  If the function is unsuccessful, it shall return NULL.
       Upon successful completion, asctime_r() shall return  a  pointer  to  a
       character  string  containing the date and time. This string is pointed
       to by the argument buf.  If the  function  is  unsuccessful,  it  shall
       return NULL.
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 asctime_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.
RATIONALE
       The standard developers decided to mark the asctime()  and  asctime_r()
       functions  obsolescent  even  though asctime() is in the ISO C standard
       due to the possibility of buffer overflow. The ISO C standard also pro-
       vides  the  strftime()  function which can be used to avoid these prob-
       lems.
FUTURE DIRECTIONS
       These functions may be removed in a future version.
SEE ALSO
       clock(), ctime(), 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                          ASCTIME(3P)