It was straight after a note that they are nonstandard functions,
which already tells the user that if portability is in mind, they
shouldn't be used, so this recommendation adds nothing in that
sense.
Also, there's a note that timelocal() should _never_ be used, due
to mktime(3) being identical and in the POSIX standard (it is also
in C99), so this note would also add nothing in that sense.
So the only uses not covered by those other notes are non-portable
uses of timegm(). In that scenario, it is an excellent function,
since it avoids races, which a home-made timegm(3) implementation
by means of standard functions would have.
A trivial implementation of timegm(3) using only standard C could
be (I didn't test it; use on your own):
// portable_timegm.c
#include <time.h>
time_t portable_timegm(struct tm *tm)
{
tm->tm_isdst = 0;
/*
* If another thread modifies the timezone during the
* execution of the line below, it will produce undefined
* behavior.
*/
return mktime(tm) - timezone;
}
Cc: Paul Eggert <eggert@xxxxxxxxxxx>
Signed-off-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
---
man3/timegm.3 | 1 -
1 file changed, 1 deletion(-)
diff --git a/man3/timegm.3 b/man3/timegm.3
index b848e83e1..0e8528b26 100644
--- a/man3/timegm.3
+++ b/man3/timegm.3
@@ -97,7 +97,6 @@ T} Thread safety MT-Safe env locale
.SH CONFORMING TO
These functions are nonstandard GNU extensions
that are also present on the BSDs.
-Avoid their use.
.SH NOTES
The
.BR timelocal ()
--
2.33.0
