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From: diamond@diamond.csl.sony.junet (Norman Diamond)
Newsgroups: comp.std.c
Subject: Re: Is this a bug in the standard?
Message-ID: <10222@socslgw.csl.sony.JUNET>
Date: 8 May 89 01:02:57 GMT
References: <189@riunite.ACA.MCC.COM>
Sender: news@csl.sony.JUNET
Reply-To: diamond@csl.sony.junet (Norman Diamond)
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In article <189@riunite.ACA.MCC.COM> rfg@riunite.UUCP (Ron Guilmette) writes:

>Well, I hope that Subject: line caught your attention.

Well, I think it's a bug in the standard.  And in C++, where you first
asked this question.  At least this one is a reasonable bug, i.e. hard
to foresee.

>Is there any completely type-safe way to declare a function
>(using function-prototype style) which can accept a
>pointer to itself as a parameter?

Seems to me that ARK's answer in comp.lang.c++ is correct; it's impossible.

But if you're content to wrap it in a struct, you get type-safety:


union bar_t;

typedef int foo_t (union bar_t);   /* gets a warning from gcc 1.32 */

typedef foo_t *foo_ptr_t;

typedef union bar_t {
    foo_ptr_t foo_ptr;
} bar_t;

foo_t foo;                         /* your prototype is done, sir */

bar_t make_bar (foo_ptr_t a_foo_ptr)
{
    bar_t my_bar;
    my_bar.foo_ptr = a_foo_ptr;
    return my_bar;
}

int foo (bar_t bar)
{
    if (bar.foo_ptr == &foo)
    {
	printf ("Hello world, it's me!\n");
	return 0;
    } else {
	printf ("Goodbye, cruel world!\n");
	return 1;
    }
}

main()
{
   foo (make_bar (&foo));
}

--
Norman Diamond, Sony Computer Science Lab (diamond%csl.sony.co.jp@relay.cs.net)
  The above opinions are my own.   |  Why are programmers criticized for
  If they're also your opinions,   |  re-inventing the wheel, when car
  you're infringing my copyright.  |  manufacturers are praised for it?