Re: failed config.h substitution

[Akim Demaille]

| Hi,
| autoconf-2.52 doesn't substitute #undef's if they are followed by a comment
| in the config.h.in. This is
|    1. a regression versus autoconf-2.13.
|    2. not documented in the manual.
| Thus it looks like a bug.

Yes, you are right.  I'm installing the following:

Index: ChangeLog
from  Akim Demaille  <address@hidden>

        * doc/autoconf.texi (Header Templates): Put also in words what the
        pictures says to assist free style readers.

Index: doc/autoconf.texi
===================================================================
RCS file: /cvsroot/autoconf/autoconf/doc/autoconf.texi,v
retrieving revision 1.704
diff -u -u -r1.704 autoconf.texi
--- doc/autoconf.texi 29 Oct 2002 12:41:16 -0000 1.704
+++ doc/autoconf.texi 29 Oct 2002 13:04:01 -0000
@@ -2471,8 +2471,9 @@
 Then you could have code like the following in @file{conf.h.in}.  On
 systems that have @file{unistd.h}, @command{configure} will @samp{#define}
 @samp{HAVE_UNISTD_H} to 1.  On other systems, the whole line will be
 commented out (in case the system predefines that symbol).
 
 @example
 @group
 /* Define as 1 if you have unistd.h.  */
 #undef HAVE_UNISTD_H
 @end group
 @end example
 
-You can then decode the configuration header using the preprocessor
-directives:
+Pay attention that @samp{#undef} is in the first column, and there is
+nothing behind @samp{HAVE_UNISTD_H}, not even white spaces.  You can
+then decode the configuration header using the preprocessor directives:
 
 @example
 @group
@@ -2487,7 +2488,9 @@
 @end example
 
 The use of old form templates, with @samp{#define} instead of
address@hidden is strongly discouraged.
address@hidden is strongly discouraged.  Similarly with old templates
+with comments on the same line as the @samp{#undef}.  Anyway, putting
+comments in preprocessor macros has never been a good idea.
 
 Since it is a tedious task to keep a template header up to date, you may
 use @command{autoheader} to generate it, see @ref{autoheader Invocation}.