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       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.


       asctime, asctime_r — convert date and time to a string


       #include <time.h>

       char *asctime(const struct tm *timeptr);
       char *asctime_r(const struct tm *restrict tm, char *restrict buf);


       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 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",
                   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 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 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


       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.


       No errors are defined.

       The following sections are informative.




       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

       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.


       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 provides the strftime() function which can be
       used to avoid these problems.


       These functions may be removed in a future version.


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

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


       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 .

       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 .