Re: Checking libraries in multiple places -- frusturated by the cache

[Lars Hecking]

Robert A. Knop Jr. writes:
> I'm fairly new to autoconf, so this may be a clueless question.
> 
> What I'm trying to do is check a few standard places for a library
> and then set a variable (*not* LIBS, but my own) based on where this
> library was found.  To this end, I have the following code in
> configure.in:
> 
>   for i in '' -L$prefix/lib -L$prefix/pgsql/lib; do
>     found=''
>     AC_MSG_RESULT("Looking for Postgres library in $i")
>     AC_CHECK_LIB(pq, PQconnectdb, found=1, found='', $i)
>     if test $found; then
>       pgsql_lib=$i
>       break
>     fi
>   done
>   if test $found; then
>     AC_MSG_RESULT("Postgres library found: $pgsql_lib")
>   else
>     AC_MSG_ERROR("Postgres library not found!")
>   fi
> 
> The problem I'm having is that after the first test fails, the generated
> configure script never really tests the other places I'm looking for the
> library-- because the failure of the first test is cached, so it thinks it
> doesn't need to do the test again!
> 
> Is there some way I can tell configure to throw out the previous cached
> value of this test before tryiing the AC_CHECK_LIB test again?  I haven't
> found anything in the documentation which would indicate how one does
> this.
> 
> I don't want to include the result of the test in LIBS, I want to set a
> different value; this is why I don't just use AC_SEARCH_LIBS.  (In any
> event, AC_SEARCH_LIBS says it sets -lsomething, not -Lsomething.)

 I have been doing something very similar for gnuplot: two macros, one
 for headers, one for libs, with a for loop around non-caching and silent
 versions of the resp. autoconf macros. See attached. I think I wrote
 this stuff before AC_SEARCH_LIBS became part of autoconf.

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