1 /* asctime a la ISO C. */ 2 3 /* 4 ** This file is in the public domain, so clarified as of 5 ** 1996-06-05 by Arthur David Olson. 6 */ 7 8 /* 9 ** Avoid the temptation to punt entirely to strftime; 10 ** strftime can behave badly when tm components are out of range, and 11 ** the output of strftime is supposed to be locale specific 12 ** whereas the output of asctime is supposed to be constant. 13 */ 14 15 /*LINTLIBRARY*/ 16 17 #include "private.h" 18 #include <stdio.h> 19 20 enum { STD_ASCTIME_BUF_SIZE = 26 }; 21 /* 22 ** Big enough for something such as 23 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648 -2147483648\n 24 ** (two three-character abbreviations, five strings denoting integers, 25 ** seven explicit spaces, two explicit colons, a newline, 26 ** and a trailing NUL byte). 27 ** The values above are for systems where an int is 32 bits and are provided 28 ** as an example; the size expression below is a bound for the system at 29 ** hand. 30 */ 31 static char buf_asctime[2*3 + 5*INT_STRLEN_MAXIMUM(int) + 7 + 2 + 1 + 1]; 32 33 /* On pre-C99 platforms, a snprintf substitute good enough for us. */ 34 #if !HAVE_SNPRINTF 35 # include <stdarg.h> 36 ATTRIBUTE_FORMAT((printf, 3, 4)) static int 37 my_snprintf(char *s, size_t size, char const *format, ...) 38 { 39 int n; 40 va_list args; 41 char stackbuf[sizeof buf_asctime]; 42 va_start(args, format); 43 n = vsprintf(stackbuf, format, args); 44 va_end (args); 45 if (0 <= n && n < size) 46 memcpy (s, stackbuf, n + 1); 47 return n; 48 } 49 # undef snprintf 50 # define snprintf my_snprintf 51 #endif 52 53 /* Publish asctime_r and ctime_r only when supporting older POSIX. */ 54 #if SUPPORT_POSIX2008 55 # define asctime_static 56 #else 57 # define asctime_static static 58 # undef asctime_r 59 # undef ctime_r 60 # define asctime_r static_asctime_r 61 # define ctime_r static_ctime_r 62 #endif 63 64 asctime_static 65 char * 66 asctime_r(struct tm const *restrict timeptr, char *restrict buf) 67 { 68 static const char wday_name[][4] = { 69 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" 70 }; 71 static const char mon_name[][4] = { 72 "Jan", "Feb", "Mar", "Apr", "May", "Jun", 73 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" 74 }; 75 register const char * wn; 76 register const char * mn; 77 int year, mday, hour, min, sec; 78 long long_TM_YEAR_BASE = TM_YEAR_BASE; 79 size_t bufsize = (buf == buf_asctime 80 ? sizeof buf_asctime : STD_ASCTIME_BUF_SIZE); 81 82 if (timeptr == NULL) { 83 strcpy(buf, "??? ??? ?? ??:??:?? ????\n"); 84 /* Set errno now, since strcpy might change it in 85 POSIX.1-2017 and earlier. */ 86 errno = EINVAL; 87 return buf; 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 year = timeptr->tm_year; 97 mday = timeptr->tm_mday; 98 hour = timeptr->tm_hour; 99 min = timeptr->tm_min; 100 sec = timeptr->tm_sec; 101 102 /* Vintage programs are coded for years that are always four bytes long 103 and may assume that the newline always lands in the same place. 104 For years that are less than four bytes, pad the output with 105 leading zeroes to get the newline in the traditional place. 106 For years longer than four bytes, put extra spaces before the year 107 so that vintage code trying to overwrite the newline 108 won't overwrite a digit within a year and truncate the year, 109 using the principle that no output is better than wrong output. 110 This conforms to ISO C and POSIX standards, which say behavior 111 is undefined when the year is less than 1000 or greater than 9999. 112 113 Also, avoid overflow when formatting tm_year + TM_YEAR_BASE. */ 114 115 if ((year <= LONG_MAX - TM_YEAR_BASE 116 ? snprintf (buf, bufsize, 117 ((-999 - TM_YEAR_BASE <= year 118 && year <= 9999 - TM_YEAR_BASE) 119 ? "%s %s%3d %.2d:%.2d:%.2d %04ld\n" 120 : "%s %s%3d %.2d:%.2d:%.2d %ld\n"), 121 wn, mn, mday, hour, min, sec, 122 year + long_TM_YEAR_BASE) 123 : snprintf (buf, bufsize, 124 "%s %s%3d %.2d:%.2d:%.2d %d%d\n", 125 wn, mn, mday, hour, min, sec, 126 year / 10 + TM_YEAR_BASE / 10, 127 year % 10)) 128 < bufsize) 129 return buf; 130 else { 131 errno = EOVERFLOW; 132 return NULL; 133 } 134 } 135 136 char * 137 asctime(register const struct tm *timeptr) 138 { 139 return asctime_r(timeptr, buf_asctime); 140 } 141 142 asctime_static 143 char * 144 ctime_r(const time_t *timep, char *buf) 145 { 146 struct tm mytm; 147 struct tm *tmp = localtime_r(timep, &mytm); 148 return tmp ? asctime_r(tmp, buf) : NULL; 149 } 150 151 char * 152 ctime(const time_t *timep) 153 { 154 /* Do not call localtime_r, as C23 requires ctime to initialize the 155 static storage that localtime updates. */ 156 struct tm *tmp = localtime(timep); 157 return tmp ? asctime(tmp) : NULL; 158 } 159