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Linux 2.6 - man page for asctime (linux section 3posix)

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

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  stan-
       dard 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 reen-
       trant 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 con-
       taining 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 local-
       time(). 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() , strp-
       time() , time() , utime() , the Base Definitions 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, 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 orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				       ASCTIME(P)


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