Re: question about whether to set CFLAGS in configure.ac

[Brian Lloyd]

On Tue, 2005-11-29 at 09:11 -0700, Ed Hartnett wrote:
> Howdy all!
> 
> I believe the common consensus is that one should not set CFLAGS in
> configure.ac.
> 
> However, I have a problem that seems to call for it. Is there a better
> way to get this working then messing with CFLAGS?
> 
> My configure allows the user to specify a location for a library, the
> HDF5 library. So they can do --with-hdf5=/some/location. I do it like
> this:
> 
> AC_ARG_WITH([hdf5],
>               [AS_HELP_STRING([--with-hdf5=<directory>],
>                               [Specify location of HDF5 library. Configure 
> will expect to find subdirs include and lib.])])
> AM_CONDITIONAL(USE_HDF5_DIR, [test ! "x$with_hdf5" = x])
> AC_SUBST(HDF5DIR, [$with_hdf5])
> 
> Then, in the automake files:
> 
> # If the user specified a root location for HDF5, use it.
> if USE_HDF5_DIR
> AM_CPPFLAGS += address@hidden@/include
> AM_LDFLAGS += address@hidden@/lib
> endif
> 

> But now I want to test during configure that I can really link to the
> HDF5 library (i.e. did they provide a valid location?). This is before
> the makefiles are even built, of course. So I try this in
> configure.ac:
> 
Try this.

saved_CFLAGS=$CFLAGS
CFLAGS="$CFLAGS -I$(HDF5DIR)/include -L$(HDF5DIR)/lib"
>    AC_CHECK_LIB([hdf5], [H5Fflush], [], [nc_hdf5_lib_missing=yes])
CFLAGS=$saved_CFLAGS

This gives the needed CFLAGS for the CHECK_LIB function, but leaves the
CFLAGS variable set as it was before this call.


Brian