preprocessor/1890: macro evaluation order prevents termination

[Zack Weinberg]

The following reply was made to PR preprocessor/1890; it has been noted by GNATS.

From: "Zack Weinberg" <zackw@stanford.edu>
To: b.i.mills@massey.ac.nz
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: preprocessor/1890: macro evaluation order prevents termination
Date: Tue, 6 Feb 2001 12:45:43 -0800

 On Tue, Feb 06, 2001 at 08:02:37PM -0000, b.i.mills@massey.ac.nz wrote:
 > 
 > cpp appears to expand macro arguments first, and then the 
 > macro. 
 
 Correct.
 
 > The result is that some macros don't terminate which did terminate
 > in earlier versions of cpp that I have used.  If outer-most-complete
 > macro expansion is used then the behaviour is cleaner and more
 > general.
 
 Sorry.  The macro expansion algorithm is specified by the C standard
 and will not change.
 
 > Eg: if leftmost syntactically correct macro is expanded, and then
 > the line is re-read the problem does not occur. I was going to use
 > the cpp to demonstrate some properties of macro expansion to my
 > class, but the version I have seems to be no good for this.
 
 I suggest you use M4 instead.
 
 zw