Hi Basil,
On Sat, Jun 07, 2025 at 09:47:49PM +0200, Basil L. Contovounesios wrote:
> I tried using Gnulib's countof macro for counting the number of
> arguments passed to a variadic function, e.g.:
>
> #define CALL(fn, args) ((fn) (countof (args), (args)))
> #define CALLN(fn, ...) CALL (fn, ((int []) {__VA_ARGS__}))Huh! This is quite interesting. :-) You may want to write about it here: <https://software.codidact.com/posts/294093> > This works with both GCC 14 and Clang 19 as long as __VA_ARGS__ > comprises compile-time constants: > > CALLN (foo, 1, 2, 3); > > However Clang fails to compile something like: > > CALLN (foo, rand(), rand(), rand()); > > with the precise diagnostics listed below. > > Am I misunderstanding something or doing something wrong? Nope, that seems to be a Clang bug. Here's a smaller reproducer of the Clang bug: alx@devuan:~/tmp$ cat cnt.c #include <stdlib.h> #include <assert.h> #define must_be(e) \ ( \ 0 * (int) sizeof( \ struct { \ static_assert(e, ""); \ int ISO_C_forbids_a_struct_with_no_members_; \ } \ ) \ ) #define is_same_type(a, b) \ ( \ __builtin_types_compatible_p(a, b) \ ) #define is_same_typeof(a, b) \ ( \ is_same_type(typeof(a), typeof(b)) \ ) #define is_array(a) \ ( \ !is_same_typeof(a, &(a)[0]) \ ) int main(void) { return must_be(is_array(((int []) {rand(), rand()}))); } alx@devuan:~/tmp$ gcc -Wall -Wextra -S cnt.c alx@devuan:~/tmp$ clang -Wall -Wextra -S cnt.c cnt.c:34:37: error: initializer element is not a compile-time constant 34 | return must_be(is_array(((int []) {rand(), rand()}))); | ^~~~~~ cnt.c:27:25: note: expanded from macro 'is_array' 27 | !is_same_typeof(a, &(a)[0]) \ | ^ cnt.c:22:29: note: expanded from macro 'is_same_typeof' 22 | is_same_type(typeof(a), typeof(b)) \ | ^ cnt.c:17:38: note: expanded from macro 'is_same_type' 17 | __builtin_types_compatible_p(a, b) \ | ^ cnt.c:9:39: note: expanded from macro 'must_be' 9 | static_assert(e, ""); \ | ^ 1 error generated. I've reported it here: <https://github.com/llvm/llvm-project/issues/143284> Have a lovely night! Alex -- <https://www.alejandro-colomar.es/>
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