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