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asctime.c revision 1.30 
      1 /*	$NetBSD: asctime.c,v 1.30 2024/01/20 14:52:49 christos 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 1.30 2024/01/20 14:52:49 christos 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 #ifndef __LIBC12_SOURCE__
     32 
     33 #ifdef __weak_alias
     34 __weak_alias(asctime_r,_asctime_r)
     35 #endif
     36 
     37 /*
     38 ** All years associated with 32-bit time_t values are exactly four digits long;
     39 ** some years associated with 64-bit time_t values are not.
     40 ** Vintage programs are coded for years that are always four digits long
     41 ** and may assume that the newline always lands in the same place.
     42 ** For years that are less than four digits, we pad the output with
     43 ** leading zeroes to get the newline in the traditional place.
     44 ** The -4 ensures that we get four characters of output even if
     45 ** we call a strftime variant that produces fewer characters for some years.
     46 ** The ISO C and POSIX standards prohibit padding the year,
     47 ** but many implementations pad anyway; most likely the standards are buggy.
     48 */
     49 static char const ASCTIME_FMT[] = "%s %s%3d %.2d:%.2d:%.2d %-4s\n";
     50 /*
     51 ** For years that are more than four digits we put extra spaces before the year
     52 ** so that code trying to overwrite the newline won't end up overwriting
     53 ** a digit within a year and truncating the year (operating on the assumption
     54 ** that no output is better than wrong output).
     55 */
     56 static char const ASCTIME_FMT_B[] = "%s %s%3d %.2d:%.2d:%.2d     %s\n";
     57 
     58 enum { STD_ASCTIME_BUF_SIZE = 26 };
     59 #endif
     60 
     61 /*
     62 ** Big enough for something such as
     63 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
     64 ** (two three-character abbreviations, five strings denoting integers,
     65 ** seven explicit spaces, two explicit colons, a newline,
     66 ** and a trailing NUL byte).
     67 ** The values above are for systems where an int is 32 bits and are provided
     68 ** as an example; the size expression below is a bound for the system at
     69 ** hand.
     70 */
     71 static char buf_ctime[2*3 + 5*INT_STRLEN_MAXIMUM(int) + 7 + 2 + 1 + 1];
     72 
     73 /* A similar buffer for ctime.
     74    C89 requires that they be the same buffer.
     75    This requirement was removed in C99, so support it only if requested,
     76    as support is more likely to lead to bugs in badly written programs.  */
     77 #ifndef __LIBC12_SOURCE__
     78 #if SUPPORT_C89
     79 # define buf_asctime buf_ctime
     80 #else
     81 static char buf_asctime[sizeof buf_ctime];
     82 #endif
     83 
     84 char *
     85 asctime_r(struct tm const *restrict timeptr, char *restrict buf)
     86 {
     87 	static const char	wday_name[][4] = {
     88 		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
     89 	};
     90 	static const char	mon_name[][4] = {
     91 		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
     92 		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
     93 	};
     94 	const char *	wn;
     95 	const char *	mn;
     96 	char			year[INT_STRLEN_MAXIMUM(int) + 2];
     97 	char result[sizeof buf_ctime];
     98 
     99 	if (timeptr == NULL) {
    100 		errno = EINVAL;
    101 		return strcpy(buf, "??? ??? ?? ??:??:?? ????\n");
    102 	}
    103 	if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
    104 		wn = "???";
    105 	else	wn = wday_name[timeptr->tm_wday];
    106 	if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
    107 		mn = "???";
    108 	else	mn = mon_name[timeptr->tm_mon];
    109 	/*
    110 	** Use strftime's %Y to generate the year, to avoid overflow problems
    111 	** when computing timeptr->tm_year + TM_YEAR_BASE.
    112 	** Assume that strftime is unaffected by other out-of-range members
    113 	** (e.g., timeptr->tm_mday) when processing "%Y".
    114 	*/
    115 	(void) strftime(year, sizeof year, "%Y", timeptr);
    116 	(void) snprintf(result,
    117 		sizeof(result),
    118 		((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
    119 		wn, mn,
    120 		timeptr->tm_mday, timeptr->tm_hour,
    121 		timeptr->tm_min, timeptr->tm_sec,
    122 		year);
    123 	if (strlen(result) < STD_ASCTIME_BUF_SIZE
    124 	    || buf == buf_ctime || 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 
    138 #endif /* !__LIBC12_SOURCE__ */
    139 
    140 char *
    141 ctime_rz(timezone_t sp, const time_t *timep, char *buf)
    142 {
    143   struct tm mytm;
    144   struct tm *tmp = localtime_rz(sp, timep, &mytm);
    145   return tmp ? asctime_r(tmp, buf) : NULL;
    146 }
    147 
    148 char *
    149 ctime_r(const time_t *timep, char *buf)
    150 {
    151   struct tm mytm;
    152   struct tm *tmp = localtime_r(timep, &mytm);
    153   return tmp ? asctime_r(tmp, buf) : NULL;
    154 }
    155 
    156 char *
    157 ctime(const time_t *timep)
    158 {
    159   return ctime_r(timep, buf_ctime);
    160 }
    161