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From: guido@mcvax.uucp (Guido van Rossum)
Newsgroups: net.lang.c++
Subject: Re: C++ problems with DMD code
Message-ID: <7081@boring.mcvax.UUCP>
Date: Mon, 22-Sep-86 18:50:51 EDT
Article-I.D.: boring.7081
Posted: Mon Sep 22 18:50:51 1986
Date-Received: Tue, 23-Sep-86 03:57:57 EDT
References: <66700003@uiucdcsp>
Reply-To: guido@boring.uucp (Guido van Rossum)
Organization: "Stamp Out BASIC" Committee, CWI, Amsterdam
Lines: 44
Apparently-To: rnews@mcvax


In article <66700003@uiucdcsp> gaulke@uiucdcsp.CS.UIUC.EDU writes:
>
>typedef	int (*ptr_fint)();
>main()
>{
>	(*((int (*)())((ptr_fint *)0x0071d700)[ 43]))( 1 );
>}
>
>I don't understand what the above jumble is, but it compiles fine using cc.
>CC, however, gives the following error message:
>
>line 4: error: un expected 1 argument for ?

You should have analyzed the jumble a bit more before complaining about
it, as it really does contain an error for CC.  The statement means the
following in C:
	1. take the constant 0x0071d700
	2. cast it to pointer to ptr_fint
	3. considering it as pointing to an array, take element 43 (of
	  type ptrf_fint)
	4. now cast it to pointer to function returning pointer to int
	5. finally call the function pointed to with an argument of 1.

The same error is emitted by CC for a more conventional fragment like this:

	extern int f();
	main() { f(1); }

	"x.c", line 2: error: un expected 1 argument for f()

The error is simply that f() is declared as a function with no argument,
but called as a function with one argument.  This is an error in C++,
but not in C.  Unfortunately C++ has chosen a different solution to cope
with this incompatibility than [proposed] ANSI C; in ANSI C, f() means
that f's arguments are unknown, and one writes f(void) to state
explicitly that f has no arguments.  In your case, the meaning of the
C code changes in C++: line 4 casts to pointer to function with no
arguments and returning pointer to int.

Your error message looks a bit strange because the function name is
unknown.  Another plea for less cryptic error messages in compilers is
in order.
-- 
	Guido van Rossum, CWI, Amsterdam <guido@mcvax.uucp>