Re: [Patch, fortran, 4.9] Use bool type instead gfc_try

["N.M. Maclaren" <nmm1 at cam dot ac dot uk>]

On Mar 22 2013, Miles Bader wrote:
> > That is another matter entirely.  The code of gcc/gfortran is supposed
> > to be compilable with other compilers, and it is foolish to make
> > unnecessary assumptions by relying on undefined behaviour.
> >
> > The simple facts are that C++ does NOT define bool to be compatible with
> > _Bool, and there are enough differences in specification and semantics
> > to make it likely that they are not the same in at least some compilers.
> > This mess has caused and still causes no end of problems for Fortran
> > interoperability and in standards like MPI.
>
> Er, maybe so, but is there actually an issue in _this_ case?

Yes.  There are many ways of resolving it, one of which is to state that
gfortran MUST be compiled in a second pass using gcc, after having built
gcc.  Another is described below.

> From original message, it sounds like these are internal compiler
> interfaces, so all that matters is that they be self-consistent, and
> there's no external ABI involved... So as long as all the code in
> question is compiled with C++ and uses C++ bool, or is compiled with
> C99 and uses _Bool, and doesn't use any functionality that isn't in
> the intersection of those two types, there shouldn't be any problem,
> right?

And that is precisely the point.  The risk isn't in either of them,
but in any interface that passes C++ bool from the front-end to C99
_Bool in the back end.  If you exclude that, there is no problem.



This is a symptom of a much wider and more serious malaise, which
I do NOT think should be discussed in this thread.  I am going to
mention it only if someone wants to contact me about it by Email,
or start a new thread.

There are much more and fouller gotchas to do with C++ and C99.
complex is worse, because there are serious differences in the
alignment requirements, and I know that affects some systems quite
badly.  But the real nasties are to do with <cmath> and errno and,
worst of all, the horrors of C99 Annex F.

My point here is that it is VERY important not to read the political
sound-bite that C++ is now based on C99 and assume that they are
actually compatible in all respects where they have 'equivalent'
facilities.  They aren't.


Regards,
Nick Maclaren.