On 2025-09-23 17:23, Robert Elz wrote:
The "one of two" is just that some return a pointer to
a struct tm, and others to a char [].
I don't see that as a plausible reading. The text says "one of two
static objects", not "a pointer of one of two types". There are two
static objects, one for localtime/gmtime and the other for
asctime/ctime, and that's pretty clear from the wording.
And I'm not the only person to read the standards this way. See, for
example, <https://codebrowser.dev/glibc/glibc/time/localtime.c.html>,
which says "C89 says that localtime and gmtime return the same pointer."
Wording to this effect has been in glibc since 1995.
Although later C standards relax this (and I'll have more to say about
that in a later email), POSIX.1-2024 still has the C89 requirement.
As you probably know, the standards did not invent this requirement. In
7th edition Unix, localtime and gmtime calls always returned the same
pointer - because localtime called gmtime, scribbled on the object
pointed to by gmtime's result, and then returned whatever pointer gmtime
returned.
