1 /* $NetBSD: asctime.c,v 1.28 2022/08/16 10:56:21 christos Exp $ */ 2 3 /* asctime and asctime_r a la POSIX and ISO C, except pad years before 1000. */ 4 5 /* 6 ** This file is in the public domain, so clarified as of 7 ** 1996-06-05 by Arthur David Olson. 8 */ 9 10 /* 11 ** Avoid the temptation to punt entirely to strftime; 12 ** the output of strftime is supposed to be locale specific 13 ** whereas the output of asctime is supposed to be constant. 14 */ 15 16 #include <sys/cdefs.h> 17 #if defined(LIBC_SCCS) && !defined(lint) 18 #if 0 19 static char elsieid[] = "@(#)asctime.c 8.5"; 20 #else 21 __RCSID("$NetBSD: asctime.c,v 1.28 2022/08/16 10:56:21 christos Exp $"); 22 #endif 23 #endif /* LIBC_SCCS and not lint */ 24 25 /*LINTLIBRARY*/ 26 27 #include "namespace.h" 28 #include "private.h" 29 #include <stdio.h> 30 31 #ifdef __weak_alias 32 __weak_alias(asctime_r,_asctime_r) 33 #endif 34 35 /* 36 ** All years associated with 32-bit time_t values are exactly four digits long; 37 ** some years associated with 64-bit time_t values are not. 38 ** Vintage programs are coded for years that are always four digits long 39 ** and may assume that the newline always lands in the same place. 40 ** For years that are less than four digits, we pad the output with 41 ** leading zeroes to get the newline in the traditional place. 42 ** The -4 ensures that we get four characters of output even if 43 ** we call a strftime variant that produces fewer characters for some years. 44 ** The ISO C and POSIX standards prohibit padding the year, 45 ** but many implementations pad anyway; most likely the standards are buggy. 46 */ 47 static char const ASCTIME_FMT[] = "%s %s%3d %.2d:%.2d:%.2d %-4s\n"; 48 /* 49 ** For years that are more than four digits we put extra spaces before the year 50 ** so that code trying to overwrite the newline won't end up overwriting 51 ** a digit within a year and truncating the year (operating on the assumption 52 ** that no output is better than wrong output). 53 */ 54 static char const ASCTIME_FMT_B[] = "%s %s%3d %.2d:%.2d:%.2d %s\n"; 55 56 enum { STD_ASCTIME_BUF_SIZE = 26 }; 57 /* 58 ** Big enough for something such as 59 ** ??? ???-2147483648 -2147483648:-2147483648:-2147483648 -2147483648\n 60 ** (two three-character abbreviations, five strings denoting integers, 61 ** seven explicit spaces, two explicit colons, a newline, 62 ** and a trailing NUL byte). 63 ** The values above are for systems where an int is 32 bits and are provided 64 ** as an example; the size expression below is a bound for the system at 65 ** hand. 66 */ 67 static char buf_asctime[2*3 + 5*INT_STRLEN_MAXIMUM(int) + 7 + 2 + 1 + 1]; 68 69 char * 70 asctime_r(const struct tm *timeptr, char *buf) 71 { 72 static const char wday_name[][4] = { 73 "Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat" 74 }; 75 static const char mon_name[][4] = { 76 "Jan", "Feb", "Mar", "Apr", "May", "Jun", 77 "Jul", "Aug", "Sep", "Oct", "Nov", "Dec" 78 }; 79 const char * wn; 80 const char * mn; 81 char year[INT_STRLEN_MAXIMUM(int) + 2]; 82 char result[sizeof buf_asctime]; 83 84 if (timeptr == NULL) { 85 errno = EINVAL; 86 return strcpy(buf, "??? ??? ?? ??:??:?? ????\n"); 87 } 88 if (timeptr->tm_wday < 0 || timeptr->tm_wday >= DAYSPERWEEK) 89 wn = "???"; 90 else wn = wday_name[timeptr->tm_wday]; 91 if (timeptr->tm_mon < 0 || timeptr->tm_mon >= MONSPERYEAR) 92 mn = "???"; 93 else mn = mon_name[timeptr->tm_mon]; 94 /* 95 ** Use strftime's %Y to generate the year, to avoid overflow problems 96 ** when computing timeptr->tm_year + TM_YEAR_BASE. 97 ** Assume that strftime is unaffected by other out-of-range members 98 ** (e.g., timeptr->tm_mday) when processing "%Y". 99 */ 100 (void) strftime(year, sizeof year, "%Y", timeptr); 101 (void) snprintf(result, 102 sizeof(result), 103 ((strlen(year) <= 4) ? ASCTIME_FMT : ASCTIME_FMT_B), 104 wn, mn, 105 timeptr->tm_mday, timeptr->tm_hour, 106 timeptr->tm_min, timeptr->tm_sec, 107 year); 108 if (strlen(result) < STD_ASCTIME_BUF_SIZE || buf == buf_asctime) 109 return strcpy(buf, result); 110 else { 111 errno = EOVERFLOW; 112 return NULL; 113 } 114 } 115 116 char * 117 asctime(const struct tm *timeptr) 118 { 119 return asctime_r(timeptr, buf_asctime); 120 } 121