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 (con-
       sult 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  IEEE Std 1003.1-2001
       defers to the ISO C standard.

       The  asctime()  function  shall  convert the broken-down time in the structure 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;
              }

       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  structure 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 reentrant. A function that is not required to be  reentrant  is  not  required  to  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()) 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.

       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
       Values for the broken-down time structure can be obtained by calling gmtime() or localtime(). This function  is  included
       for  compatibility with older implementations, and does not support localized date and time formats.  Applications should
       use strftime() to achieve maximum portability.

       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
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       clock(),  ctime(), difftime(), gmtime(), localtime(), mktime(), strftime(), strptime(), time(), utime(), the Base Defini-
       tions volume of IEEE Std 1003.1-2001, <time.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003  Edition,  Standard  for
       Information  Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. 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.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                   ASCTIME(3P)