Re: Conditionally set CXXFLAGS based on directory via 1 configure.ac?

[Eric Blake]

On 07/27/2011 04:13 PM, Xochitl Lunde wrote:
> Is there a nice way to conditionally add -fno-exceptions to CXXFLAGS for the "Source Dir" 
> from configure.ac or elsewhere?  I am sure I can go to each library under "Source Dir" 
> and put -fno-exceptions in AM_CXXFLAGS, but is there a correct way to do it in configure.ac?

The nicest way to to this is to not change CXXFLAGS, but to instead 
AC_SUBST two different variables for the difference in which compiler 
options you want (you _did_ test that $CXX supports -fno-exceptions 
before blindly adding it to CXXFLAGS, right?  Not all the world is g++). 
 Then, in the appropriate Makefile.am files, modify AM_CXXFLAGS to 
include the appropriate substituted variables.

See how coreutils does things: in the top level configure.ac, it does an 
AC_SUBST of WERROR_CFLAGS, WARN_CFLAGS, and GNULIB_WARN_CFLAGS - three 
distinct subsets of flags that were all tested on whether they were 
supported by the current compiler, and where WERROR_CFLAGS is 
conditional on whether you requested configure --enable-gcc-warnings. 
Then, src/Makefile.am sets AM_CFLAGS to $(WARN_CFLAGS) $(WERROR_CFLAGS), 
while lib/Makefile.am uses the less-strict AM_CFLAGS += 
$(GNULIB_WARN_CFLAGS) $(WERROR_CFLAGS).

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org