"Niels Möller" wrote:

Roberto Bagnara bagnara@cs.unipr.it writes:

...

it would be nice to be able to write `--enable-exceptions' in the GMP configure command line so that, if GMP is compiled with GCC, the `-fexceptions' option is used. This is necessary to have, e.g., `bad_alloc' thrown when virtual memory is exhausted and most serious C++ GMP users will want to do that. Of course, the default can/should be `--disable-exceptions'.

I think that having compile time options that change these kinds of behaviour is asking for trouble. Sooner or later you'll have a system where GMP is installed, and you don't know which way it was compiled, or you have both variants installed in different places and accidentally link with the wrong one. And it probably gets even worse with dynamic linking.

If you want exception raising to be optional, I think you should put the two variants into different namespaces, and then you can have compile time options for building either or both variants.

An alternative is of course to "always" build with exceptions, and say that the GMP C++ ABI includes raising exceptions under certain circumastances. You could leave a compile time option for disabling exceptions (changing the ABI), but then you'd have to shoot any distributor that ships GMP libraries compiled in that incompatible way.

Dear Niels,

what I am asking for is a feature and I am willing to do everything it requires to minimize the chance of troubles. That is why I sent a message to this list. The feature is very important for our application (a C++ library for the manipulation of convex polyhedra) and I believe it is important for all those C++ applications where the exhaustion of virtual memory cannot simply be handled by writing a message and aborting. The feature is so important that I have already done the modifications I am proposing to GMP 3.1.1. What I would like to avoid is having to distribute tar archives and RPMs of the modified version to the users of our library.

I realize that there is a potential for troubles but I also believe that solutions can be found. For the people doing `make install' we could make sure the exceptions-enabled versions of GMP are installed under the basename, say `libgmp_e'. This is not uncommon: on the Red Hat system I am using I have both the packages

glibc-devel-2.2.4-19 glibc-profile-2.2.4-19

installed. The first contains /usr/lib/libc.a (the standard thing) while the second has /usr/lib/libc_p.a (the same library compiled with the profiling options). The same can be done for shared libraries, of course.

(And at last, you should be able to get what you want with

CXXFLAGS=-fexceptions && ./configure && make

without using any new configure options).

No, CXXFLAGS has nothing to do with what we are talking about. In fact

1) GMP is written in C; 2) -fexceptions is the GCC default for the compilation of C++ sources, so it will be OK even when GMP will include the new C++ interface.

Perhaps you meant

CFLAGS=-fexceptions && ./configure && make

but this is also a very bad idea in GMP 3.1.1 (the current release), since `-fexceptions' will _replace_ any other compilation option so that a good portion of the nice work done by the configure script is simply lost. In other words, on the machine I am using this very moment, I would compile GMP with `-fexceptions' instead of `-g -O -fomit-frame-pointer -mcpu=pentiumpro', and these (apart from the strange coexistence of `-g' and `-fomit-frame-pointer') are also compilation options I definitely want. All the best,

Roberto