> From: Michael Richardson <[email protected]>
> Sent: Thursday, 31 March, 2022 14:18
>
> Michael Wojcik <[email protected]> wrote:
> > #if defined OPENSSL_SYS_WINDOWS
> > # include <shared/netiodef.h>
> > #else
> > # include <netinet/ip6.h>
> > #endif
>
> But, don't all the OPENSSL_* macros expand to 0/1, anyway, so we actually
> just want #if OPENSSL_SYS_WINDOWS?
I did a quick grep through the source for 1.1.1k (just because that's what I
had to hand; we've actually just finished updating my portfolio to 1.1.1n), and
there's a mix of #if OPENSSL_SYS_WINDOWS and #if defined(OPENSSL_SYS_WINDOWS).
apps/s_client.c uses the latter, for example.
Actually, in the context of #if expressions, unrecognized tokens expand to 0
anyway:
After all replacements due to macro expansion and the defined unary
operator have been performed, all remaining identifiers are replaced
with the pp-number 0...
(ISO 9899:1999 6.10.1 #3)
So defining a macro used for conditional inclusion to the value 0 is kind of a
bad idea, since that means there's different behavior between #if FOO and #if
defined FOO. Much better to not define it and get the default value of 0 if you
want to turn it off.
But that said, #if OPENSSL_SYS_WINDOWS is safer for the same reason: it doesn't
matter whether it's defined as 0, or not defined at all.
The "defined" operator is overused in C source generally. It's good for things
like header inclusion guards. It's not really a good choice for most other
cases of conditional inclusion.
--
Michael Wojcik
