77
88/*
99** Avoid the temptation to punt entirely to strftime;
10+ ** strftime can behave badly when tm components are out of range, and
1011** the output of strftime is supposed to be locale specific
1112** whereas the output of asctime is supposed to be constant.
1213*/
1617#include "private.h"
1718#include <stdio.h>
1819
19- /*
20- ** All years associated with 32-bit time_t values are exactly four digits long;
21- ** some years associated with 64-bit time_t values are not.
22- ** Vintage programs are coded for years that are always four digits long
23- ** and may assume that the newline always lands in the same place.
24- ** For years that are less than four digits, we pad the output with
25- ** leading zeroes to get the newline in the traditional place.
26- ** The -4 ensures that we get four characters of output even if
27- ** we call a strftime variant that produces fewer characters for some years.
28- ** This conforms to recent ISO C and POSIX standards, which say behavior
29- ** is undefined when the year is less than 1000 or greater than 9999.
30- */
31- static char const ASCTIME_FMT [] = "%s %s%3d %.2d:%.2d:%.2d %-4s\n" ;
32- /*
33- ** For years that are more than four digits we put extra spaces before the year
34- ** so that code trying to overwrite the newline won't end up overwriting
35- ** a digit within a year and truncating the year (operating on the assumption
36- ** that no output is better than wrong output).
37- */
38- static char const ASCTIME_FMT_B [] = "%s %s%3d %.2d:%.2d:%.2d %s\n" ;
39-
4020enum { STD_ASCTIME_BUF_SIZE = 26 };
4121/*
4222** Big enough for something such as
@@ -50,14 +30,24 @@ enum { STD_ASCTIME_BUF_SIZE = 26 };
5030*/
5131static char buf_asctime [2 * 3 + 5 * INT_STRLEN_MAXIMUM (int ) + 7 + 2 + 1 + 1 ];
5232
53- /* A similar buffer for ctime.
54- C89 requires that they be the same buffer.
55- This requirement was removed in C99, so support it only if requested,
56- as support is more likely to lead to bugs in badly written programs. */
57- #if SUPPORT_C89
58- # define buf_ctime buf_asctime
59- #else
60- static char buf_ctime [sizeof buf_asctime ];
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
6151#endif
6252
6353/* Publish asctime_r and ctime_r only when supporting older POSIX. */
@@ -84,38 +74,59 @@ asctime_r(struct tm const *restrict timeptr, char *restrict buf)
8474 };
8575 register const char * wn ;
8676 register const char * mn ;
87- char year [INT_STRLEN_MAXIMUM (int ) + 2 ];
88- char result [sizeof buf_asctime ];
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 );
8981
9082 if (timeptr == NULL ) {
83+ strcpy (buf , "??? ??? ?? ??:??:?? ????\n" );
84+ /* Set errno now, since strcpy might change it in
85+ POSIX.1-2017 and earlier. */
9186 errno = EINVAL ;
92- return strcpy ( buf , "??? ??? ?? ??:??:?? ????\n" ) ;
87+ return buf ;
9388 }
9489 if (timeptr -> tm_wday < 0 || timeptr -> tm_wday >= DAYSPERWEEK )
9590 wn = "???" ;
9691 else wn = wday_name [timeptr -> tm_wday ];
9792 if (timeptr -> tm_mon < 0 || timeptr -> tm_mon >= MONSPERYEAR )
9893 mn = "???" ;
9994 else mn = mon_name [timeptr -> tm_mon ];
100- /*
101- ** Use strftime's %Y to generate the year, to avoid overflow problems
102- ** when computing timeptr->tm_year + TM_YEAR_BASE.
103- ** Assume that strftime is unaffected by other out-of-range members
104- ** (e.g., timeptr->tm_mday) when processing "%Y".
105- */
106- strftime (year , sizeof year , "%Y" , timeptr );
107- /*
108- ** We avoid using snprintf since it's not available on all systems.
109- */
110- sprintf (result ,
111- ((strlen (year ) <= 4 ) ? ASCTIME_FMT : ASCTIME_FMT_B ),
112- wn , mn ,
113- timeptr -> tm_mday , timeptr -> tm_hour ,
114- timeptr -> tm_min , timeptr -> tm_sec ,
115- year );
116- if (strlen (result ) < STD_ASCTIME_BUF_SIZE
117- || buf == buf_ctime || buf == buf_asctime )
118- return strcpy (buf , result );
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 ;
119130 else {
120131 errno = EOVERFLOW ;
121132 return NULL ;
@@ -140,5 +151,8 @@ ctime_r(const time_t *timep, char *buf)
140151char *
141152ctime (const time_t * timep )
142153{
143- return ctime_r (timep , buf_ctime );
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 ;
144158}
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