Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ucbcad!ucbvax!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.lang.c
Subject: Clarifications on ANSI C nits
Message-ID: <3725@hoptoad.uucp>
Date: 24 Dec 87 02:06:49 GMT
Organization: Nebula Consultants in San Francisco
Lines: 71

While testing the GNU C compiler using the MetaWare C Validation Suite,
I found a bunch of things that are not clearly marked in the Oct 86 copy
of the C draft standard.  I'm interested in clarification from the group
and/or from the standards committee on these:

 * I've heard a rumor that in newer drafts, hex escape sequences inside
 strings are no longer limited to 3 characters, e.g. "abc\x00345"
produces "abcE" since 'E' (0x45) is (char)0x00345.  This strikes me as odd.

 * Is a "const void *" a void pointer?  Is a "volatile void *"?  Howabout
a "const volatile void *"?  Howabout a "void *const"?  A "pointer to void"
gets special treatment in a few places (e.g. in assignment) but it's not
clear whether these are "pointers to void".  (Howabout "volatile void
*noalias const foo", just for fun?)

 * It appears from the text in section 3.5.3.3 that variable-argument-list
functions can ONLY be defined in the 

	foo(int c, float bar, ...)

syntax, and not in the

	foo(c, bar, ...)
		int c;
		float bar;

syntax.  GCC implements it this way.  However, this makes it impossible
to support <varargs.h> since no existing code uses the new declaration
method.  It also seems to be a silly inconsistency.

 * Though a union can now be initialized, you can only initialize one
member, but you have to surround it with { } anyway.  To correctly
initialize the structure below, ALL the braces used are required:

	struct s{union {int x,y; int z;} u; int q;} s[2] =
		{{{1}, 2}, {{3}, 4}}; 

I would have expected:

		{1, 2, 3, 4};

to work, but the wording of the standard does not support it.  Furthermore,
the standard does not allow extra braces (e.g. around 2 and 4, or around the
whole thing), so you have to get it exactly right.  Is this what was intended?

(These next two aren't from the validation suite.)

 * When calling a function, side effects caused by evaluating the arguments
must be complete before the call takes place.  What about side effects
caused by evaluating the function name?  Ron Light gave this example:

	typedef int (*Inst)();          /* machine instruction */
	Inst *pc;                       /* program counter during execution */

	execute(p)                      /* run the machine */
	Inst *p;
	{
		for(pc = p;;)
			(*(*pc++))();
	}

If I reference "pc" from inside a function called from the forloop, is
its value guaranteed to be incremented, to not be incremented, or not
guaranteed?

 * Are null statements (extra semicolons) allowed between declarations?
Between struct/union members' declarations?
-- 
{pyramid,ptsfa,amdahl,sun,ihnp4}!hoptoad!gnu			  gnu@toad.com
  I forsee a day when there are two kinds of C compilers: standard ones and 
  useful ones ... just like Pascal and Fortran.  Are we making progress yet?
	-- ASC:GUTHERY%slb-test.csnet