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From: travis@mojo.columbia.edu (Travis Lee Winfrey)
Newsgroups: gnu.g++,comp.lang.c++
Subject: Re: Use of yacc/bison and g++
Message-ID: <5850@columbia.edu>
Date: 29 Aug 88 17:32:50 GMT
References: <8808240932.AA08805@prep.ai.mit.edu>
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Reply-To: travis@mojo.cs.columbia.edu
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Organization: Columbia University Department of Computer Science
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In article <8808240932.AA08805@prep.ai.mit.edu> gordon%stats.ucl.ac.uk@NSS.CS.UCL.AC.UK writes:
>Should it be possible to include C++ statements in a
>yacc file, "compile" with yacc (or better bison?) and compile the
>result with g++?

Yes, it *should* be possible.  I've been doing that all summer with Yacc/CC.  I
haven't used bison/g++, only because of the bugs and general flakiness of g++.
(spare me the flames, I'm sure it will become a fine compiler.)  The action
statements in yacc are only translated, with $$, $1, etc., being rewritten
appropriately.  Getting the typing right can be a mild problem.  Generally, it
works exactly as you would expect it to.

The biggest problems I had were with CC, not with g++, and they both involved
static initializers:

1) when I used the default main() in liby.a, main() wasn't compiled by CC, so
_main() wasn't called from main(), so any static initializers of variables were
*not* called.  This causes subtle bugs in your programs if you don't use
streams IO, and immediate core dumps if you do.

2) peripherally related to YACC, I had problems with an initial yylex() which
used cin, didn't use cout, and dumped core immediately on trying to read a
character.  This is easy to repeat, as 

	#include <stream.h>
	main()
	{ char ch;
	  cin >> ch ; 
	}

dumps core with our streams library.  If any reference to cout is made, even if
it can never be called (e.g., "if ( x && ! x ) cout.put(x);"), then the program
doesn't dump core.  CC always failed, but g++ handled it correctly.

I tracked this down to the tied_to field of the cin structure, which contains
the address of cout.  cout wasn't initialized because it was never called.  I
didn't follow the bug into the cout routines, because I could patch it here:
since tied_to was not called if it was null, the fix was just to add "(void)
cin.tie(0);" to the program.  This bug has probably been fixed in later
versions of streams, but it's a pretty special case.

t
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