Re: Finding library procedures in /usr/local/lib/

[Ralf Wildenhues]

Hello Gerald,

* Gerald I. Evenden wrote on Fri, Apr 03, 2009 at 08:11:22PM CEST:
> One added note, that bothers me a little.
> 
> If the system checks for an entry being present in a particular iibrary by 
> compiling/linking a test program using the function *and* linking to the 
> specified library,----> what if the library under test heavily references 
> another library such as -lm??  IF -lm is not in the test run would the test 
> not fail???????  Thus the entry under test fails also.

I haven't read the thread in full, but this is probably the issue
bothering you:

AC_CHECK_LIB and AC_SEARCH_LIBS both have an optional 5th argument where
one can supply additional needed libraries.  So of libfoo needs libm,
then a check for libfoo could look like

  AC_SEARCH_LIBS([function_from_libfoo], [foo], [], [], [-lm])

and after this macro, $LIBS would contain -lfoo if the test was
successful.  Of course, you can check for both in sequence,
  AC_SEARCH_LIBS([cos], [m])
  AC_SEARCH_LIBS([function_from_libfoo], [foo])

and in this case you don't need to specify -lm in the second macro,
because the first macro will have added that to $LIBS (and $LIBS is used
for linking).

And yes, library linking order *always* matters.  The bugs are just more
obscure with GNU/Linux and shared linking than they are under other
circumstances.

Cheers,
Ralf