Re: [Libguestfs] [libnbd PATCH v3 01/29] use space consistently in function and function-like macro invocations
On Fri, Feb 17, 2023 at 11:49:58AM +0000, Richard W.M. Jones wrote:
On Wed, Feb 15, 2023 at 01:48:39PM -0600, Eric Blake wrote:
> In my experience with GNU code (which this is not), the style I've
> seen there is to omit () whenever possible, as in:
>
> #if defined __GNUC__
>
> or even
>
> #ifdef __GNUC__
I didn't know this was possible.
I checked it. GCC and clang with -std=c89 and -std=c99 allow this, so
I don't object.
Although we don't support (eg) MSVC do you know if this is really
standard C?
C17 section 6.10.1P1:
"The expression that controls conditional inclusion shall be an
integer constant expression except that: identifiers (including those
lexically identical to keywords) are interpreted as described
below;168) and it may contain unary operator expressions of the form
defined identifier
or
defined ( identifier )
which evaluate to 1 if the identifier is currently defined as a macro
name (that is, if it is predefined or if it has been the subject of a
#define preprocessing directive without an intervening #undef
directive with the same subject identifier), 0 if it is not."
Presumably similar in the upcoming C23, although I didn't check it.
It's standard.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org