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asctime.c revision 1.24.2.1 
      1 /*	$NetBSD: asctime.c,v 1.24.2.1 2018/05/21 04:35:55 pgoyette Exp $	*/
      2 
      3 /* asctime and asctime_r a la POSIX and ISO C, except pad years before 1000.  */
      4 
      5 /*
      6 ** This file is in the public domain, so clarified as of
      7 ** 1996-06-05 by Arthur David Olson.
      8 */
      9 
     10 /*
     11 ** Avoid the temptation to punt entirely to strftime;
     12 ** the output of strftime is supposed to be locale specific
     13 ** whereas the output of asctime is supposed to be constant.
     14 */
     15 
     16 #include <sys/cdefs.h>
     17 #if defined(LIBC_SCCS) && !defined(lint)
     18 #if 0
     19 static char	elsieid[] = "@(#)asctime.c	8.5";
     20 #else
     21 __RCSID("$NetBSD: asctime.c,v 1.24.2.1 2018/05/21 04:35:55 pgoyette Exp $");
     22 #endif
     23 #endif /* LIBC_SCCS and not lint */
     24 
     25 /*LINTLIBRARY*/
     26 
     27 #include "namespace.h"
     28 #include "private.h"
     29 #include <stdio.h>
     30 
     31 #ifdef __weak_alias
     32 __weak_alias(asctime_r,_asctime_r)
     33 #endif
     34 
     35 /*
     36 ** Some systems only handle "%.2d"; others only handle "%02d";
     37 ** "%02.2d" makes (most) everybody happy.
     38 ** At least some versions of gcc warn about the %02.2d;
     39 ** we conditionalize below to avoid the warning.
     40 */
     41 /*
     42 ** All years associated with 32-bit time_t values are exactly four digits long;
     43 ** some years associated with 64-bit time_t values are not.
     44 ** Vintage programs are coded for years that are always four digits long
     45 ** and may assume that the newline always lands in the same place.
     46 ** For years that are less than four digits, we pad the output with
     47 ** leading zeroes to get the newline in the traditional place.
     48 ** The -4 ensures that we get four characters of output even if
     49 ** we call a strftime variant that produces fewer characters for some years.
     50 ** The ISO C and POSIX standards prohibit padding the year,
     51 ** but many implementations pad anyway; most likely the standards are buggy.
     52 */
     53 #ifdef __GNUC__
     54 #define ASCTIME_FMT	"%s %s%3d %2.2d:%2.2d:%2.2d %-4s\n"
     55 #else /* !defined __GNUC__ */
     56 #define ASCTIME_FMT	"%s %s%3d %02.2d:%02.2d:%02.2d %-4s\n"
     57 #endif /* !defined __GNUC__ */
     58 /*
     59 ** For years that are more than four digits we put extra spaces before the year
     60 ** so that code trying to overwrite the newline won't end up overwriting
     61 ** a digit within a year and truncating the year (operating on the assumption
     62 ** that no output is better than wrong output).
     63 */
     64 #ifdef __GNUC__
     65 #define ASCTIME_FMT_B	"%s %s%3d %2.2d:%2.2d:%2.2d     %s\n"
     66 #else /* !defined __GNUC__ */
     67 #define ASCTIME_FMT_B	"%s %s%3d %02.2d:%02.2d:%02.2d     %s\n"
     68 #endif /* !defined __GNUC__ */
     69 
     70 #define STD_ASCTIME_BUF_SIZE	26
     71 /*
     72 ** Big enough for something such as
     73 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
     74 ** (two three-character abbreviations, five strings denoting integers,
     75 ** seven explicit spaces, two explicit colons, a newline,
     76 ** and a trailing NUL byte).
     77 ** The values above are for systems where an int is 32 bits and are provided
     78 ** as an example; the define below calculates the maximum for the system at
     79 ** hand.
     80 */
     81 #define MAX_ASCTIME_BUF_SIZE	(2*3+5*INT_STRLEN_MAXIMUM(int)+7+2+1+1)
     82 
     83 static char	buf_asctime[MAX_ASCTIME_BUF_SIZE];
     84 
     85 char *
     86 asctime_r(const struct tm *timeptr, char *buf)
     87 {
     88 	static const char	wday_name[][4] = {
     89 		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
     90 	};
     91 	static const char	mon_name[][4] = {
     92 		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
     93 		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
     94 	};
     95 	const char *	wn;
     96 	const char *	mn;
     97 	char			year[INT_STRLEN_MAXIMUM(int) + 2];
     98 	char			result[MAX_ASCTIME_BUF_SIZE];
     99 
    100 	if (timeptr == NULL) {
    101 		errno = EINVAL;
    102 		return strcpy(buf, "??? ??? ?? ??:??:?? ????\n");
    103 	}
    104 	if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
    105 		wn = "???";
    106 	else	wn = wday_name[timeptr->tm_wday];
    107 	if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
    108 		mn = "???";
    109 	else	mn = mon_name[timeptr->tm_mon];
    110 	/*
    111 	** Use strftime's %Y to generate the year, to avoid overflow problems
    112 	** when computing timeptr->tm_year + TM_YEAR_BASE.
    113 	** Assume that strftime is unaffected by other out-of-range members
    114 	** (e.g., timeptr->tm_mday) when processing "%Y".
    115 	*/
    116 	(void) strftime(year, sizeof year, "%Y", timeptr);
    117 	(void) snprintf(result,
    118 		sizeof(result),
    119 		((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
    120 		wn, mn,
    121 		timeptr->tm_mday, timeptr->tm_hour,
    122 		timeptr->tm_min, timeptr->tm_sec,
    123 		year);
    124 	if (strlen(result) < STD_ASCTIME_BUF_SIZE || buf == buf_asctime)
    125 		return strcpy(buf, result);
    126 	else {
    127 		errno = EOVERFLOW;
    128 		return NULL;
    129 	}
    130 }
    131 
    132 char *
    133 asctime(const struct tm *timeptr)
    134 {
    135 	return asctime_r(timeptr, buf_asctime);
    136 }
    137