transport conditionals to other files (was: (no subject))

[Ralf Wildenhues]

Hello Ting,

* ting xie wrote on Thu, Sep 16, 2010 at 10:23:45PM CEST:
> How are you? It is quite a long time since we talked last time. 

Yes.  I'm just fine, thanks!  (There are many other helpful readers
on this list, by the way ...)

> I got a new question about autoconf now. Suppose I have defined a
> conditional variable in configure.ac file as follows. 
> 
> AM_CONDITIONAL([FOO], [test x$foo = xtrue])  
> 
> I have another file test.inc.in file, if I want to put the condition
> foo into this .inc.in file, how can I do that? 

Hmm, you cannot put the condition into another file right away, as for
one, the shell variable $foo will not have any meaning there.  However,
if the file is instantiated by config.status (i.e., config.status reads
FILE.inc.in and produces FILE.inc from it), then you can use a
substituted variable; put AC_SUBST([foo]) in configure.ac, and @foo@ in
FILE.inc.in, and it will get replaced with the value of $foo.

> BTW, I do not understand this kind of postfix .inc.in file. May you
> also give me some explanation on this kind of files if you have time? 

The .in postfix usually indicates that this file is read by
config.status to create a file without the .in postfix; see
  info Autoconf "Configuration Files"

for more information.

Hope that helps.

Cheers,
Ralf