What the hell is dynamic_cast for?

[Daniel Pitts]

Yes. Don't confuse legal/illegal with succeeded/failed. An
illegal dynamic_cast won't compile. But a legal dynamic_cast
can fail at runtime, in which case, it either returns a null
pointer (pointer cast) or throws an exception (reference cast).

Just for sake of completeness, what does dynamic_cast do with an already
null pointer?

p = 0;
pD = dynamic_cast<Derived *>(p); // exception, sigsegv, or null?

 

[Kai-Uwe Bux]

Just for sake of completeness, what does dynamic_cast do with an already
null pointer?

p = 0;
pD = dynamic_cast<Derived *>(p); // exception, sigsegv, or null?

If the argument to dynamic_cast<T*> is 0, the cast evaluates to 0. See
[5.2.7/4].


Best

Kai-Uwe Bux

 

[James Kanze]

Just for sake of completeness, what does dynamic_cast do with
an already null pointer?

p = 0;
pD = dynamic_cast<Derived *>(p); // exception, sigsegv, or null?

It's guaranteed to return a null pointer. This is true for all
pointer casts, in fact. (Which means that even static_cast may
require some actual code to be executed.)