asctime man page on Oracle

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ASCTIME(3P)		   POSIX Programmer's Manual		   ASCTIME(3P)

       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
       IEEE Std 1003.1-2001 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",
		      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 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 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.

       Upon  successful	 completion,  asctime()	 shall return a pointer to the

       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.


       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

       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.



       clock(),	 ctime(),  difftime(),	gmtime(), localtime(), mktime(), strf‐
       time(), strptime(), time(), utime(), the	 Base  Definitions  volume  of
       IEEE Std 1003.1-2001, <time.h>

       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, Copyright (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 .

IEEE/The Open Group		     2003			   ASCTIME(3P)

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