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Re: problem with cached values
From: |
Ralf Wildenhues |
Subject: |
Re: problem with cached values |
Date: |
Wed, 10 Jan 2007 19:38:58 +0100 |
User-agent: |
Mutt/1.5.13 (2006-08-11) |
Hello Vincent,
* Vincent Torri wrote on Tue, Dec 26, 2006 at 06:39:27PM CET:
[...]
> I've installed STLport 5.1 in /usr/local. So, the first check (in /usr)
> returns a warning, and then STLport is searched in /usr/local. The result
> of the configure script is the following:
>
> checking stl/config/user_config.h usability... no
> checking stl/config/user_config.h presence... no
> checking for stl/config/user_config.h... no
> configure: WARNING: STLport headers not in /usr/include/stlport
> checking for stl/config/user_config.h... (cached) no
> configure: WARNING: STLport headers not in /usr/local/include/stlport
> configure: error: "STLport is needed !"
> Can someone explain what the problem is, and then what kind of solution
> there is to such problem ?
Autoconf caching assumes that AC_CHECK_HEADERS checks do not depend on
other state. (This is at least somewhat reasonable: all other header
checks could change if you change CPPFLAGS after them.)
You have two ways to fix your macro:
1)
Put a
unset ac_cv_header_std_config_user_config_h
before your test.
2)
Roll your own manual test (using AC_COMPILE_IFELSE, AC_PREPROC_IFELSE,
AC_LANG_PROGRAM etc.) that uses no caching or a manual form of
unambiguous caching.
The first has the advantage of being simple, but the disadvantages of
being more expensive for rechecks (e.g., `./config.status --recheck'),
and a wee bit less portable, see
<http://www.gnu.org/software/autoconf/manual/html_node/Limitations-of-Builtins.html#index-g_t_0040command_007bunset_007d-1259>.
But that's probably not a problem for you in practice. In any case your
users will see an error if unset does not work.
The second solution is a bit more work. ;-)
I think Eric covered the rest of your mail.
Cheers,
Ralf
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