Mouse wrote in
<202211021508.laa26...@stone.rodents-montreal.org>:
|> Suppose you create a struct tm _without_ gmtime(3) or localtime(3),
|> using designated initializers or memset for zero-initialization, with
|> only what is included in POSIX:
|
|> struct tm tm = {
|> .tm_sec = 56,
|> .tm_min = 34,
|> .tm_hour = 12,
|> .tm_mday = 1,
|> .tm_mon = 12 - 1, /* December */
|> .tm_year = 2021 - 1900,
|> .tm_wday = 3, /* Wednesday */
|> .tm_yday = 334, /* zero-based day of year (%j - 1) */
|> .tm_isdst = 0,
|>};
|
|This is fine. But using memset is not; if struct tm contains a pointer
|or a floating-point value, setting it to all-0-bits may produce a trap
|representation - or, possibly worse, a valid value that means something
|different from what you intend.
|
|Unless POSIX was stupid enough to mandate that all-bits-0 is nil for
|any pointer type and something well-defined for floating-point. (I'd
The former is definetely true. (Or will be.)
And i think on the TZ list it just came up it is generally true
for all "modern" machines. (Except for C++ member pointers which
may be -1 (in parts, i hated their double-pointer size).)
|be surprised by that, but standards bodies have surprised me often
|enough in the past.) Certainly C doesn't, at least not as of C99 - I
|don't have a copy of anything newer.
Ah. ISO C.
--steffen
|
|Der Kragenbaer, The moon bear,
|der holt sich munter he cheerfully and one by one
|einen nach dem anderen runter wa.ks himself off
|(By Robert Gernhardt)
