time/asctime.c

   1 /* Copyright (C) 1991-2021 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3
   4    The GNU C Library is free software; you can redistribute it and/or
   5    modify it under the terms of the GNU Lesser General Public
   6    License as published by the Free Software Foundation; either
   7    version 2.1 of the License, or (at your option) any later version.
   8
   9    The GNU C Library is distributed in the hope that it will be useful,
  10    but WITHOUT ANY WARRANTY; without even the implied warranty of
  11    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12    Lesser General Public License for more details.
  13
  14    You should have received a copy of the GNU Lesser General Public
  15    License along with the GNU C Library; if not, see
  16    <https://www.gnu.org/licenses/>.  */
  17
  18 #include "../locale/localeinfo.h"
  19 #include <errno.h>
  20 #include <limits.h>
  21 #include <stdio.h>
  22 #include <time.h>
  23
  24 /* This is defined in locale/C-time.c in the GNU libc.  */
  25 extern const struct __locale_data _nl_C_LC_TIME attribute_hidden;
  26 #define ab_day_name(DAY) (_nl_C_LC_TIME.values[_NL_ITEM_INDEX (ABDAY_1)+(DAY)].string)
  27 #define ab_month_name(MON) (_nl_C_LC_TIME.values[_NL_ITEM_INDEX (ABMON_1)+(MON)].string)
  28
  29 static const char format[] = "%.3s %.3s%3d %.2d:%.2d:%.2d %d\n";
  30 static char result[              3+1+ 3+1+20+1+20+1+20+1+20+1+20+1 + 1];
  31
  32
  33 static char *
  34 asctime_internal (const struct tm *tp, char *buf, size_t buflen)
  35 {
  36   if (tp == NULL)
  37     {
  38       __set_errno (EINVAL);
  39       return NULL;
  40     }
  41
  42   /* We limit the size of the year which can be printed.  Using the %d
  43      format specifier used the addition of 1900 would overflow the
  44      number and a negative vaue is printed.  For some architectures we
  45      could in theory use %ld or an evern larger integer format but
  46      this would mean the output needs more space.  This would not be a
  47      problem if the 'asctime_r' interface would be defined sanely and
  48      a buffer size would be passed.  */
  49   if (__glibc_unlikely (tp->tm_year > INT_MAX - 1900))
  50     {
  51     eoverflow:
  52       __set_errno (EOVERFLOW);
  53       return NULL;
  54     }
  55
  56   int n = __snprintf (buf, buflen, format,
  57                       (tp->tm_wday < 0 || tp->tm_wday >= 7
  58                        ? "???" : ab_day_name (tp->tm_wday)),
  59                       (tp->tm_mon < 0 || tp->tm_mon >= 12
  60                        ? "???" : ab_month_name (tp->tm_mon)),
  61                       tp->tm_mday, tp->tm_hour, tp->tm_min,
  62                       tp->tm_sec, 1900 + tp->tm_year);
  63   if (n < 0)
  64     return NULL;
  65   if (n >= buflen)
  66     goto eoverflow;
  67
  68   return buf;
  69 }
  70
  71
  72 /* Like asctime, but write result to the user supplied buffer.  The
  73    buffer is only guaranteed to be 26 bytes in length.  */
  74 char *
  75 __asctime_r (const struct tm *tp, char *buf)
  76 {
  77   return asctime_internal (tp, buf, 26);
  78 }
  79 weak_alias (__asctime_r, asctime_r)
  80
  81
  82 /* Returns a string of the form "Day Mon dd hh:mm:ss yyyy\n"
  83    which is the representation of TP in that form.  */
  84 char *
  85 asctime (const struct tm *tp)
  86 {
  87   return asctime_internal (tp, result, sizeof (result));
  88 }
  89 libc_hidden_def (asctime)