Handling of exception specification violations

[Nathan Sidwell]

Peter Schuller wrote:
> Hello,
> 
> In C++, I would like to take advantage of throw() clauses for their
> documentative value (and possible future value if gcc implements
> checked exceptions). At the same time however, I want to *usefully*
> handle the throwing of unexpected exceptions (where "useful" includes
> being able to inspect the exception in question).
> 
> Toward this end I have a couple of questions that my Googling has not
> helped:
> 
> * gcc has an option -fno-enforce-eh-specs which has pretty much the effect
>   I would want because it allows for generic top-level catch() statements
>   that exit with a useful error message. The man-page says the compiler
>   "will still optimize based on the exception specifications". Should I
>   interpret this as saying it is *unsafe* to enable this option with
>   code that *does* throw unexpected exceptions? If not, is it guaranteed
>   to *be* safe?

the code will be unsafe.  If an exception is thrown out of a throw () function, 
the effects will be undefined.

> * providing user-defined behavior for std::unexpected() (as exemplified
>   at [1]) would be an alternative aswell - *if* I can obtain a reference
>   to the exception during runtime. Is there some way (standard or
>   gcc-specific) to do this?

This is target specific.  Note that the exception object might be foreign (a non 
C++ object).  Look at unwind.h for details.

nathan

-- 
Nathan Sidwell    ::   http://www.codesourcery.com   ::     CodeSourcery LLC
nathan@codesourcery.com    ::     http://www.planetfall.pwp.blueyonder.co.uk