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| author | Alejandro Colomar <alx@kernel.org> | 2024-08-24 00:51:55 +0200 |
|---|---|---|
| committer | Alejandro Colomar <alx@kernel.org> | 2024-08-30 13:10:54 +0200 |
| commit | bd576aaf5fce40100133c1d48c02eacbf25594c8 (patch) | |
| tree | 768cca02f467a60a21247ccff545b50a650c6d03 /man/man3/ctime.3 | |
| parent | 9fdca71e4aba3605caa88b0c9eff3dc2c3f6fcfe (diff) | |
| download | man-pages-bd576aaf5fce40100133c1d48c02eacbf25594c8.tar.gz | |
ctime.3: EXAMPLES: Document how to detect invalid or ambiguous times
This example documents how to detect some corner cases of mktime(3),
such as DST transitions and other jumps in the calendar.
Link: <https://www.redhat.com/en/blog/brief-history-mktime>
Cc: DJ Delorie <dj@redhat.com>
Cc: Carlos O'Donell <carlos@redhat.com>
Cc: Paul Eggert <eggert@cs.ucla.edu>
Signed-off-by: Alejandro Colomar <alx@kernel.org>
Diffstat (limited to 'man/man3/ctime.3')
| -rw-r--r-- | man/man3/ctime.3 | 78 |
1 files changed, 77 insertions, 1 deletions
diff --git a/man/man3/ctime.3 b/man/man3/ctime.3 index 53abab6d94..acd6f15650 100644 --- a/man/man3/ctime.3 +++ b/man/man3/ctime.3 @@ -467,6 +467,14 @@ For example, a change in the timezone definition may cause a clock time to be repeated or skipped without a corresponding DST change. .SH EXAMPLES +The program below defines a wrapper that +allows detecting invalid and ambiguous times, +with +.B EINVAL +and +.BR ENOTUNIQ , +respectively. +.P The following shell session shows sample runs of the program: .P .in +4n @@ -482,6 +490,7 @@ $ .RB $\~ "./a.out 2024 08 23 00 17 53 \-1" ; 1724365073 .RB $\~ "./a.out 2024 08 23 00 17 53 0" ; +a.out: my_mktime: Invalid argument 1724368673 .RB $\~ "./a.out 2024 08 23 00 17 53 1" ; 1724365073 @@ -491,12 +500,15 @@ $ .RB $\~ "./a.out 2024 02 23 00 17 53 0" ; 1708643873 .RB $\~ "./a.out 2024 02 23 00 17 53 1" ; +a.out: my_mktime: Invalid argument 1708640273 $ .RB $\~ "./a.out 2023 03 26 02 17 53 \-1" ; +a.out: my_mktime: Invalid argument 1679793473 $ .RB $\~ "./a.out 2023 10 29 02 17 53 \-1" ; +a.out: my_mktime: Name not unique on network 1698542273 .RB $\~ "./a.out 2023 10 29 02 17 53 0" ; 1698542273 @@ -504,6 +516,7 @@ $ 1698538673 $ .RB $\~ "./a.out 2023 02 29 12 00 00 \-1" ; +a.out: my_mktime: Invalid argument 1677668400 .EE .SS Program source: mktime.c @@ -511,13 +524,17 @@ $ .\" SRC BEGIN (mktime.c) .EX #include <err.h> +#include <errno.h> #include <stdint.h> #include <stdio.h> #include <stdlib.h> +#include <string.h> #include <time.h> \& #define is_signed(T) ((T) \-1 < 1) \& +time_t my_mktime(struct tm *tp); +\& int main(int argc, char *argv[]) { @@ -539,10 +556,13 @@ main(int argc, char *argv[]) tm.tm_sec = atoi(*p++); tm.tm_isdst = atoi(*p++); \& + errno = 0; tm.tm_wday = \-1; - t = mktime(&tm); + t = my_mktime(&tm); if (tm.tm_wday == \-1) err(EXIT_FAILURE, "mktime"); + if (errno == EINVAL || errno == ENOTUNIQ) + warn("my_mktime"); \& if (is_signed(time_t)) printf("%jd\[rs]n", (intmax_t) t); @@ -551,6 +571,62 @@ main(int argc, char *argv[]) \& exit(EXIT_SUCCESS); } +\& +time_t +my_mktime(struct tm *tp) +{ + int e, isdst; + time_t t; + struct tm tm; + unsigned char wday[sizeof(tp\->tm_wday)]; +\& + e = errno; +\& + tm = *tp; + isdst = tp\->tm_isdst; +\& + memcpy(wday, &tp\->tm_wday, sizeof(wday)); + tp\->tm_wday = \-1; + t = mktime(tp); + if (tp\->tm_wday == \-1) { + memcpy(&tp\->tm_wday, wday, sizeof(wday)); + return \-1; + } +\& + if (isdst == \-1) + tm.tm_isdst = tp\->tm_isdst; +\& + if ( tm.tm_sec != tp\->tm_sec + || tm.tm_min != tp\->tm_min + || tm.tm_hour != tp\->tm_hour + || tm.tm_mday != tp\->tm_mday + || tm.tm_mon != tp\->tm_mon + || tm.tm_year != tp\->tm_year + || tm.tm_isdst != tp\->tm_isdst) + { + errno = EINVAL; + return t; + } +\& + if (isdst != \-1) + goto out; +\& + tm = *tp; + tm.tm_isdst = !tm.tm_isdst; +\& + tm.tm_wday = \-1; + mktime(&tm); + if (tm.tm_wday == \-1) + goto out; +\& + if (tm.tm_isdst != tp\->tm_isdst) { + errno = ENOTUNIQ; + return t; + } +out: + errno = e; + return t; +} .EE .\" SRC END .SH SEE ALSO |