lib/libc/stdtime/asctime.c

   1 /*
   2 ** This file is in the public domain, so clarified as of
   3 ** 1996-06-05 by Arthur David Olson.
   4 */
   5
   6 /*
   7 ** Avoid the temptation to punt entirely to strftime;
   8 ** the output of strftime is supposed to be locale specific
   9 ** whereas the output of asctime is supposed to be constant.
  10 **
  11 ** $FreeBSD: head/contrib/tzcode/stdtime/asctime.c 214411 2010-10-27 07:14:46Z edwin $
  12 */
  13 /*LINTLIBRARY*/
  14
  15 #include "namespace.h"
  16 #include "private.h"
  17 #include "un-namespace.h"
  18 #include "tzfile.h"
  19
  20 /*
  21 ** Some systems only handle "%.2d"; others only handle "%02d";
  22 ** "%02.2d" makes (most) everybody happy.
  23 ** At least some versions of gcc warn about the %02.2d;
  24 ** we conditionalize below to avoid the warning.
  25 */
  26 /*
  27 ** All years associated with 32-bit time_t values are exactly four digits long;
  28 ** some years associated with 64-bit time_t values are not.
  29 ** Vintage programs are coded for years that are always four digits long
  30 ** and may assume that the newline always lands in the same place.
  31 ** For years that are less than four digits, we pad the output with
  32 ** leading zeroes to get the newline in the traditional place.
  33 ** The -4 ensures that we get four characters of output even if
  34 ** we call a strftime variant that produces fewer characters for some years.
  35 ** The ISO C 1999 and POSIX 1003.1-2004 standards prohibit padding the year,
  36 ** but many implementations pad anyway; most likely the standards are buggy.
  37 */
  38 #ifdef __GNUC__
  39 #define ASCTIME_FMT     "%.3s %.3s%3d %2.2d:%2.2d:%2.2d %-4s\n"
  40 #else /* !defined __GNUC__ */
  41 #define ASCTIME_FMT     "%.3s %.3s%3d %02.2d:%02.2d:%02.2d %-4s\n"
  42 #endif /* !defined __GNUC__ */
  43 /*
  44 ** For years that are more than four digits we put extra spaces before the year
  45 ** so that code trying to overwrite the newline won't end up overwriting
  46 ** a digit within a year and truncating the year (operating on the assumption
  47 ** that no output is better than wrong output).
  48 */
  49 #ifdef __GNUC__
  50 #define ASCTIME_FMT_B   "%.3s %.3s%3d %2.2d:%2.2d:%2.2d     %s\n"
  51 #else /* !defined __GNUC__ */
  52 #define ASCTIME_FMT_B   "%.3s %.3s%3d %02.2d:%02.2d:%02.2d     %s\n"
  53 #endif /* !defined __GNUC__ */
  54
  55 #define STD_ASCTIME_BUF_SIZE    26
  56 /*
  57 ** Big enough for something such as
  58 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648     -2147483648\n
  59 ** (two three-character abbreviations, five strings denoting integers,
  60 ** seven explicit spaces, two explicit colons, a newline,
  61 ** and a trailing ASCII nul).
  62 ** The values above are for systems where an int is 32 bits and are provided
  63 ** as an example; the define below calculates the maximum for the system at
  64 ** hand.
  65 */
  66 #define MAX_ASCTIME_BUF_SIZE    (2*3+5*INT_STRLEN_MAXIMUM(int)+7+2+1+1)
  67
  68 static char     buf_asctime[MAX_ASCTIME_BUF_SIZE];
  69
  70 /*
  71 ** A la ISO/IEC 9945-1, ANSI/IEEE Std 1003.1, 2004 Edition.
  72 */
  73
  74 char *
  75 asctime_r(const struct tm * __restrict timeptr, char * __restrict buf)
  76 {
  77         static const char       wday_name[][3] = {
  78                 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"
  79         };
  80         static const char       mon_name[][3] = {
  81                 "Jan", "Feb", "Mar", "Apr", "May", "Jun",
  82                 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"
  83         };
  84         char            year[INT_STRLEN_MAXIMUM(int) + 2];
  85         char            result[MAX_ASCTIME_BUF_SIZE];
  86         const char *    wn;
  87         const char *    mn;
  88
  89         if (timeptr == NULL) {
  90                 errno = EINVAL;
  91                 return strcpy(buf, "??? ??? ?? ??:??:?? ????\n");
  92         }
  93         if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK)
  94                 wn = "???";
  95         else    wn = wday_name[timeptr->tm_wday];
  96         if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR)
  97                 mn = "???";
  98         else    mn = mon_name[timeptr->tm_mon];
  99         /*
 100         ** Use strftime's %Y to generate the year, to avoid overflow problems
 101         ** when computing timeptr->tm_year + TM_YEAR_BASE.
 102         ** Assume that strftime is unaffected by other out-of-range members
 103         ** (e.g., timeptr->tm_mday) when processing "%Y".
 104         */
 105         strftime(year, sizeof year, "%Y", timeptr);
 106         snprintf(result, sizeof result,
 107                 ((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B),
 108                 wn, mn,
 109                 timeptr->tm_mday, timeptr->tm_hour,
 110                 timeptr->tm_min, timeptr->tm_sec,
 111                 year);
 112         if (strlen(result) < STD_ASCTIME_BUF_SIZE || buf == buf_asctime) {
 113                 return strcpy(buf, result);
 114         } else {
 115                 errno = EOVERFLOW;
 116                 return NULL;
 117         }
 118 }
 119
 120 /*
 121 ** A la ISO/IEC 9945-1, ANSI/IEEE Std 1003.1, 2004 Edition.
 122 */
 123
 124 char *
 125 asctime(const struct tm *timeptr)
 126 {
 127         return asctime_r(timeptr, buf_asctime);
 128 }