Re: pgsql: Assume that we have signed integral types and flexible array mem

Peter Geoghegan <pg@bowt.ie> writes:
> I see this change to c.h:

> +/*
> + * We require C99, hence the compiler should understand flexible array
> + * members.  However, for documentation purposes we still consider it to be
> + * project style to write "field[FLEXIBLE_ARRAY_MEMBER]" not just "field[]".
> + * When computing the size of such an object, use "offsetof(struct s, f)"
> + * for portability.  Don't use "offsetof(struct s, f[0])", as this doesn't
> + * work with MSVC and with C++ compilers.
> + */
> +#define FLEXIBLE_ARRAY_MEMBER  /* empty */

> Why not just get rid of the FLEXIBLE_ARRAY_MEMBER hack altogether?

As I said in the comment, I think it's good style.

Even if you disagree, we shouldn't remove the macro, because that will
just gratuitously break third-party code.

> I don't think that we need it as a way of drawing attention to the
> fact that "offsetof(struct s, f[0])" should not be used. That's not
> idiomatic style anyway. If somebody makes this mistake, then I believe
> that their code will reliably fail to compile once it hits CF Tester
> or the buildfarm.

I'm not 100% sure that aspect of the comment is still correct anyway.
I just copied that advice from the Autoconf output --- but it might well
be referring to the behavior of pre-C99 MSVC versions.  However, if it
is correct, why are you sure that violating the advice will lead to
a compile error and not to silently-wrong size calculations?

            regards, tom lane