Re: [PATCH] add relation and block-level filtering to pg_waldump

On Thu, Mar 24, 2022 at 9:53 AM Peter Eisentraut
<peter(dot)eisentraut(at)enterprisedb(dot)com> wrote:
> On 21.03.22 05:55, Thomas Munro wrote:
> > [04:30:50.630] pg_waldump.c:963:26: error: format ‘%u’ expects
> > argument of type ‘unsigned int *’, but argument 3 has type ‘ForkNumber
> > *’ [-Werror=format=]
> > [04:30:50.630] 963 | if (sscanf(optarg, "%u",
> > &config.filter_by_relation_forknum) != 1 ||
> > [04:30:50.630] | ~^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> > [04:30:50.630] | | |
> > [04:30:50.630] | | ForkNumber *
> > [04:30:50.630] | unsigned int *
> >
> > And now that this gets to the CompilerWarnings CI task, it looks like
> > GCC doesn't like an enum as a scanf %u destination (I didn't see that
> > warning locally when I compiled the above fixup because clearly Clang
> > is cool with it...). Probably needs a temporary unsigned int to
> > sscanf into first.
>
> That's because ForkNum is a signed type. You will probably succeed if
> you use "%d" instead.

Erm, is that really OK? C says "Each enumerated type shall be
compatible with char, a signed integer type, or an
unsigned integer type. The choice of type is implementation-defined,
but shall be capable of representing the values of all the members of
the enumeration." It could even legally vary from enum to enum,
though in practice most compilers probably just use ints all the time
unless you use weird pragma pack incantation. Therefore I think you
need an intermediate variable with the size and signedness matching the
format string, if you're going to scanf directly into it, which
David's V6 did.