Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ucsd!rutgers!att!ulysses!andante!alice!ark
From: ark@alice.UUCP (Andrew Koenig)
Newsgroups: comp.lang.c
Subject: Re: AT&T C compilers
Keywords: C compiler,bug?
Message-ID: <8972@alice.UUCP>
Date: 26 Feb 89 13:13:08 GMT
References: <569@marob.MASA.COM> <1071@auspex.UUCP>
Organization: AT&T Bell Laboratories, Liberty Corner NJ
Lines: 43

In article <1071@auspex.UUCP>, guy@auspex.UUCP (Guy Harris) writes:

[discussion about     extern int bob(double (*)());    ]

> (Deep breath, count to 5)  Prototypes are a relatively new feature in C
> implementations.  Some compilers do not support them.  The "Portable C
> Compiler", upon which many (most?) UNIX C compilers - including the ones
> AT&T supplies - are based, does not support them.

> The declaration in question appears to be correct, except that it says
> the argument taken by "bob" is a pointer to a function returning
> "double", but doesn't say what sort of arguments that function takes.  I
> think this is legal, however.

Sure it is -- the arguments of the function are unspecified so it's
up to the programmer to get them right when calling it.

> I don't know whether it's legal C++ or not; if it is, I suspect the
> declaration says, in C++, that the function to which the pointer points
> takes no arguments (since C++, unlike C, does not have the notion of
> "old-style" function declarations where an empty argument list indicates
> that the types of the arguments are unknown).

Exactly right.

It is legal C++, by the way, but presently available C++ translator
do not support it -- it is hard to parse.

You can achieve the same effect by a semantic hack:

	typedef (*doublefp)();
	extern double bob(doublefp);

or by a syntactic hack:

	extern double bob(auto double(*)());

The (not yet generally available) C++ translator on my machine supports
the original form of the declaration just fine, so I imagine it will
also be supported by the next version released.
-- 
				--Andrew Koenig
				  ark@europa.att.com