Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!mit-eddie!cybvax0!amit
From: amit@cybvax0.UUCP (Amit Green)
Newsgroups: comp.lang.c++
Subject: Bug (Cybermation #1) with fix: lost declaration.
Message-ID: <1507@cybvax0.UUCP>
Date: 3 Jan 88 04:49:40 GMT
Reply-To: amit@cybvax0.UUCP (Amit Green)
Organization: Cybermation, Inc., Cambridge, MA
Lines: 55

Problem:
	double x (a, b, c, d)
	long a;
	double b, c;
	char d;
	{ return a + b + c + d;		//  Avoid "not used" error message
	}

Produces the following code (shortened & comment added):
	"", line 1: warning: old style definition of x()

	/* <<cfront 1.2.1 2/16/87>> */
	double x (_au0_a , _au0_b , _au0_c , _au0_d )
	long _au0_a ;
	double _au0_b ;
	int _au0_c ;		//  <=  This line is wrong, should be a double
	char _au0_d ;
	{ return (((_au0_a + _au0_b )+ _au0_c )+ _au0_d );
	}
	;

Notice:
	The declaration of 'c' as a double is lost (and it defaults to
	an int).  In fact the following may be presented to the compiler:

	double x (a, b, c, d)
	long a;
	double b, c;
	char d;
	short c;	//  Redeclare 'c' as the declaration above was lost
	{ return a + b + c + d;		//  Avoid "not used" error message
	}

Analysis:
	gram.y (from cfront 1.2.1) has a bug:
	line 1: /*ident	"@(#)cfront:src/gram.y	1.10" */
	line 1225:                error("FD inAL (%n)",$<pn>2);
	line 1226:	       else if ($1)
	line 1227:		  $<nl>1->add($<pn>2);

	The statement should be '$<nl>1->add_list($<pn>2)' since '$<pn>2'
	may be list, as it is in the declaration 'double b, c'.

	The problem exist only when '$<nl>1' is already a list (as it is
	from the declaration 'long a'), and is then appended to
	again (as it is in the declaration 'char d').

Final Comment:
	This bug may have been mentioned before, I am not sure.  I have
	printed out all the previous message since comp.lang.c++ started
	(even from when it was called net.lang.c++), and am still in
	the process of reading them; if this is a repeat, sorry.

				Amit Green
				{harvard,mit-eddie}!cybvax0!amit