Re: Module with preprocessor utilities

[Bruno Haible]

[Adding back bug-gnulib in CC]

Marc Nieper-Wißkirchen wrote:
> > Marc Nieper-Wißkirchen wrote:
> > > For example, do we want to encourage the writing of
> > > sophisticated macros like the TRACE macros in chapter 16 of (the IMHO
> > > opinionated) book Modern C ([1]).
> >
> > This TRACE macro is an interesting academic example. I say "academic",
> > because who wants a trace statement that outputs only numbers, no string
> > arguments? And once you allow string arguments, you notice that you need
> > a varargs function, not a macro.
> 
> Unless you want to use _Generic of C11, you probably need a varargs function.

Do you have an idea which compilers support _Generic and which don't?

> > > [1] https://gforge.inria.fr/frs/download.php/latestfile/5298/ModernC.pdf
> >
> > Will I learn something by reading this book, or will it spoil me? :-)
> 
> There's possibly something to learn but I don't think that one will be
> spoiled. :) A number of things look interesting but also quite
> Idiosyncratic to me. Due to these things, I wouldn't suggest the book
> to a beginner who wants to learn C, though.
> 
> For example, the author suggests to use a prototype like
> 
> void foo (X x [static 1]);
> 
> to denote that the argument "x" is a non-null pointer to a value of
> type "X". While this seems to be the intent of "[static 1]" in the C
> standard, it doesn't generalize well when "X" does not denote a
> complete type. In that case, one has to resort to
> 
> void foo (X *x);
> 
> as pointers to incomplete types are fine.

Also, if that's the intent of the syntax, it has been overlooked by the
GCC developers. See:

============================ decl.c ============================
#include <stddef.h>

extern void foo1 (double x [static 1]);
extern void foo2 (double x []) __attribute__ ((__nonnull__(1)));

int bar ()
{
  foo1 (NULL);
  foo2 (NULL);
  return 1;
}
=================================================================
$ gcc -Wall -S decl.c
decl.c: In function 'bar':
decl.c:9:3: warning: null argument where non-null required (argument 1) 
[-Wnonnull]
    9 |   foo2 (NULL);
      |   ^~~~

(This is with gcc 10.1.0.)

clang, OTOH, produces warnings for both foo1 and foo2.

But I won't spend time to report a GCC bug on this, because - as you said -
without the ability to declare a pointer to an incomplete type or a 'void *'
as non-null, this language feature is worthless.

Bruno