Re: [Boost-users] [Exception] How do I inherit custom exception hierarchy from std::runtime_error rather than from std::exception?

On Wed, Nov 27, 2013 at 10:39 PM, Eric Prud'hommeaux wrote:

On Nov 27, 2013 9:52 PM, "Emil Dotchevski" wrote:

...

On Wed, Nov 27, 2013 at 8:19 AM, Egor Tensin wrote:

...

The issue that's confusing me arose from my intention of inheriting my exception classes from std::runtime_error rather than from std::exception. It seemed logical to me, as my exceptions are really runtime errors; getting something meaningful via what() also seemed like a good idea. However, this doesn't compile:

<cut>

...

struct foo_error : virtual boost::exception, virtual std::runtime_error { explicit foo_error(const char *const what) : std::runtime_error(what) { }

Yes, you'd have to use non-virtual inheritance if you want to be able to pass the what parameter like this. However, I would recommend deriving virtually from std::exception and using different exception types rather than different what strings for different failures. It is usually appropriate to override what() and implement it in terms of diagnostic_information_what (see

www.boost.org/doc/libs/release/libs/exception/doc/diagnostic_information_what.html.)

Your advice makes sense to me but I'm curious what semantics you write off, either explicit in the runtime_error definition or implied by library or development tool interpretation of runtime_error.

I've never seen anyone catch a std::runtime_error for any other reason than to print the what() string; and std::exception is just as good for that. The other thing is, virtual inheritance is used in exception class hierarchies to enable safe use of multiple inheritance, but std::runtime_error doesn't derive virtually from std::exception. This makes std::runtime_error and virtual inheritance mutually exclusive in my book. -- Emil Dotchevski Reverge Studios, Inc. http://www.revergestudios.com/reblog/index.php?n=ReCode