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asctime.c revision 1.26 
      1 /*	$NetBSD: asctime.c,v 1.26 2019/01/27 02:08:35 pgoyette Exp $	*/
      2 
      3 /* asctime and asctime_r a la POSIX and ISO C, except pad years before 1000.  */
      4 
      5 /* asctime and asctime_r a la POSIX and ISO C, except pad years before 1000.  */
      6 
      7 /*
      8 ** This file is in the public domain, so clarified as of
      9 ** 1996-06-05 by Arthur David Olson.
     10 */
     11 
     12 /*
     13 ** Avoid the temptation to punt entirely to strftime;
     14 ** the output of strftime is supposed to be locale specific
     15 ** whereas the output of asctime is supposed to be constant.
     16 */
     17 
     18 #include <sys/cdefs.h>
     19 #if defined(LIBC_SCCS) && !defined(lint)
     20 #if 0
     21 static char	elsieid[] = "@(#)asctime.c	8.5";
     22 #else
     23 __RCSID("$NetBSD: asctime.c,v 1.26 2019/01/27 02:08:35 pgoyette Exp $");
     24 #endif
     25 #endif /* LIBC_SCCS and not lint */
     26 
     27 /*LINTLIBRARY*/
     28 
     29 #include "namespace.h"
     30 #include "private.h"
     31 #include <stdio.h>
     32 
     33 #ifdef __weak_alias
     34 __weak_alias(asctime_r,_asctime_r)
     35 #endif
     36 
     37 /*
     38 ** Some systems only handle "%.2d"; others only handle "%02d";
     39 ** "%02.2d" makes (most) everybody happy.
     40 ** At least some versions of gcc warn about the %02.2d;
     41 ** we conditionalize below to avoid the warning.
     42 */
     43 /*
     44 ** All years associated with 32-bit time_t values are exactly four digits long;
     45 ** some years associated with 64-bit time_t values are not.
     46 ** Vintage programs are coded for years that are always four digits long
     47 ** and may assume that the newline always lands in the same place.
     48 ** For years that are less than four digits, we pad the output with
     49 ** leading zeroes to get the newline in the traditional place.
     50 ** The -4 ensures that we get four characters of output even if
     51 ** we call a strftime variant that produces fewer characters for some years.
     52 ** The ISO C and POSIX standards prohibit padding the year,
     53 ** but many implementations pad anyway; most likely the standards are buggy.
     54 */
     55 #ifdef __GNUC__
     56 #define ASCTIME_FMT	"%s %s%3d %2.2d:%2.2d:%2.2d %-4s\n"
     57 #else /* !defined __GNUC__ */
     58 #define ASCTIME_FMT	"%s %s%3d %02.2d:%02.2d:%02.2d %-4s\n"
     59 #endif /* !defined __GNUC__ */
     60 /*
     61 ** For years that are more than four digits we put extra spaces before the year
     62 ** so that code trying to overwrite the newline won't end up overwriting
     63 ** a digit within a year and truncating the year (operating on the assumption
     64 ** that no output is better than wrong output).
     65 */
     66 #ifdef __GNUC__
     67 #define ASCTIME_FMT_B	"%s %s%3d %2.2d:%2.2d:%2.2d     %s\n"
     68 #else /* !defined __GNUC__ */
     69 #define ASCTIME_FMT_B	"%s %s%3d %02.2d:%02.2d:%02.2d     %s\n"
     70 #endif /* !defined __GNUC__ */
     71 
     72 #define STD_ASCTIME_BUF_SIZE	26
     73 /*
     74 ** Big enough for something such as
     75 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
     76 ** (two three-character abbreviations, five strings denoting integers,
     77 ** seven explicit spaces, two explicit colons, a newline,
     78 ** and a trailing NUL byte).
     79 ** The values above are for systems where an int is 32 bits and are provided
     80 ** as an example; the define below calculates the maximum for the system at
     81 ** hand.
     82 */
     83 #define MAX_ASCTIME_BUF_SIZE	(2*3+5*INT_STRLEN_MAXIMUM(int)+7+2+1+1)
     84 
     85 static char	buf_asctime[MAX_ASCTIME_BUF_SIZE];
     86 
     87 char *
     88 asctime_r(const struct tm *timeptr, char *buf)
     89 {
     90 	static const char	wday_name[][4] = {
     91 		"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
     92 	};
     93 	static const char	mon_name[][4] = {
     94 		"Jan", "Feb", "Mar", "Apr", "May", "Jun",
     95 		"Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
     96 	};
     97 	const char *	wn;
     98 	const char *	mn;
     99 	char			year[INT_STRLEN_MAXIMUM(int) + 2];
    100 	char			result[MAX_ASCTIME_BUF_SIZE];
    101 
    102 	if (timeptr == NULL) {
    103 		errno = EINVAL;
    104 		return strcpy(buf, "??? ??? ?? ??:??:?? ????\n");
    105 	}
    106 	if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
    107 		wn = "???";
    108 	else	wn = wday_name[timeptr->tm_wday];
    109 	if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
    110 		mn = "???";
    111 	else	mn = mon_name[timeptr->tm_mon];
    112 	/*
    113 	** Use strftime's %Y to generate the year, to avoid overflow problems
    114 	** when computing timeptr->tm_year + TM_YEAR_BASE.
    115 	** Assume that strftime is unaffected by other out-of-range members
    116 	** (e.g., timeptr->tm_mday) when processing "%Y".
    117 	*/
    118 	(void) strftime(year, sizeof year, "%Y", timeptr);
    119 	(void) snprintf(result,
    120 		sizeof(result),
    121 		((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
    122 		wn, mn,
    123 		timeptr->tm_mday, timeptr->tm_hour,
    124 		timeptr->tm_min, timeptr->tm_sec,
    125 		year);
    126 	if (strlen(result) < STD_ASCTIME_BUF_SIZE || buf == buf_asctime)
    127 		return strcpy(buf, result);
    128 	else {
    129 		errno = EOVERFLOW;
    130 		return NULL;
    131 	}
    132 }
    133 
    134 char *
    135 asctime(const struct tm *timeptr)
    136 {
    137 	return asctime_r(timeptr, buf_asctime);
    138 }
    139