On 29 Jun 2017, at 19:16, Mark Millard <[email protected]> wrote: > > On 2017-Jun-29, at 5:54 AM, Konstantin Belousov <kostikbel at gmail.com> > wrote: >> >> On Thu, Jun 29, 2017 at 12:47:10PM +0200, Dimitry Andric wrote: >>> One nasty problem with this is that it is not possible to figure out at >>> compile time what the size of time_t is. You always need some sort of >>> configure-time test, and an external define. >> >> It is arguably possible, with constexpr. > > I took Dimitry's wording as probably referring to > testing the size in the C/C++ preprocessor like > the original code tests for __LP64__ being defined > vs. not to control what it does: extending that to > involve more preprocessor tests to pick from more > code blocks. (But it is a guess given his wording.)
Yeah, what I meant is that the code does something like:
#if __LP64__
static_assert(whatever, "foo");
#else
static_assert(otherthing, "bar");
#endif
where __LP64__ was erroneously thought to determine whether time_t was
64-bit. You cannot replace this with something like the following C++11
construct, though:
constexpr bool time_t_64bit = sizeof(time_t) == 8;
if (time_t_64bit)
static_assert(true, "time_t is OK");
else
static_assert(false, "time_t is bad");
because both static assertions will be evaluated at compile time, and
one of them will fail.
In any case, Eric Fiselier already had some sort of patch lined up, but
I slacked off on trying it out. Sorry about that. :)
-Dimitry
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