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Re: [Tinycc-devel] Tinycc-devel Digest, Vol 103, Issue 1
From: |
Ben |
Subject: |
Re: [Tinycc-devel] Tinycc-devel Digest, Vol 103, Issue 1 |
Date: |
Wed, 02 Nov 2011 20:32:18 +0000 |
On Wed, 2011-11-02 at 17:29 +0100, Robert Clausecker wrote:
> Am Mittwoch, den 02.11.2011, 12:00 -0400 schrieb Ben Bacarisse
>
> > > It seems that I discovered a bug in tcc. ANSI C allows declaration
> > of
> > > prototypes containing function pointers like this:
> > >
> > > void traverse(mystruct_t*, void(mycontent_t*));
> > >
> > > tcc currently rejects this giving an error "')' expected". This
> > > equivalent prototype works:
> > >
> > > void traverse(mystruct_t*,void(*)(mycontent_t*));
> > >
> > > Is this a bug or a feature?
> >
> > The two prototypes are not equivalent. The first is a syntax error
> > but
> > the second one is fine -- provided you wanted to pass a pointer to a
> > function that takes a mycontent_t pointer and returns nothing.
>
> I asked some folks on #c on freenode and they told me to tell you that
> section 3.5.4.3, paragraph 9 of the C89 standard specifies that this is
> allowed.
Yes, they are correct. It's unusual to see such types in a prototype
but they are indeed valid. Sad to say, I actually knew this, but for
some reason chose to forget about it.
> (Why else would both gcc and clang allow the first declaration
> with or without the -std=c89 or -ansi flag?) Quote:
>
> For each parameter declared with function or array type, its
> type for these comparisons is the one that results from
> conversion to a pointer type, as in $3.7.1.
C99 is the current standard, but it has similar wording. It's been
split out into its own paragraph (p8 of 6.7.5.3) and it now reads:
"A declaration of a parameter as 'function returning type' shall
be adjusted to 'pointer to function returning type', as in 6.3.2.1."
> I am not an expert on the C spec, but please have a look at it.
>
> Here is an easier testcase that compiles:
>
> int foo(int,int,int(int,int));
> int foo(int a,int b,int f(int,int)) { return f(a,b); }
It's also permitted via a typedef:
typedef int func_type(int, int);
int foo(int, int, func_type);
Personally, I always prefer to make the pointer explicit, but its
perfectly valid not to.
--
Ben Bacarisse