Path: utzoo!mnetor!uunet!husc6!cmcl2!rutgers!sdcsvax!ucbvax!hoptoad!gnu
From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: comp.lang.c
Subject: Kinds of code broken by ANSI C
Message-ID: <3724@hoptoad.uucp>
Date: 23 Dec 87 02:23:38 GMT
References: <4668@pyr.gatech.EDU> <2046@haddock.ISC.COM>
Organization: Nebula Consultants in San Francisco
Lines: 47

karl@haddock.ISC.COM (Karl Heuer) wrote:
> Can you really find a lot of examples of code that will be broken (not just
> deprecated) by the new standard?  No fair using code that was already
> nonportable under K&R but just happened to work on your compiler.
> 
> The only one that springs to my mind is mktemp("fooXXXXXX") (because it's no
> longer safe to assume that string literals are writable).

I have been porting 4.3BSD through gcc and finding a bunch of things.
Many are nonportabilities -- preprocessor abuse and referencing members
of other structures are the most common -- but some are not.  One that
comes to mind is functions that do:

	foo()
	{
		extern int errno;
		errno = 0; ...
	}

	bar()
	{
		if (errno) ...
	}

ANSI C defines the "extern int errno;" to be local to foo(), so bar()
must redeclare errno before it can use it.  K&R defined it to be global.

Another is that various programs used the identifier "signed".

Another is programs that had unbalanced quotes inside #if 0.

Another is programs that do:

	typedef int flag;
	foo(flag)
		int flag;
	{...}

which has gotten hard to parse in ANSI C and is now disallowed.

I can show you Unix source code that uses all these features.
I will probably end up writing a paper for Usenix about it...
-- 
{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