Re: dynamic_cast undefined behavior
On 7/19/2013 8:02 PM, kawninzx6@googlemail.com wrote:
Hi C++ experts,
Is it ever safe to dereference a NULL pointer? Specifically,
I'm curious about dereferencing NULL during dynamic_cast.
Contrived example code:
// includes omitted
class BaseFoo
{
public:
virtual ~BaseFoo() {}
};
class Foo : public BaseFoo {};
void process(int& i) { ... }
void process(Foo& foo) { ... }
BaseFoo* getFoo() { ... }
I assume you meant:
BaseFoo* getFoo() { return 0; }
int main()
{
int *i = NULL;
void process(*i); // (1)
That's not safe. You will probably get an OS exception at run-time for
trying to read memory at 0.
try
{
process(dynamic_cast<Foo&>(*getFoo())); // (2)
That's not safe also. Ditto with the above.
}
catch (const std::exception&)
{
// ignore bad_cast exception
}
return 0;
}
(1) - This is always undefined behavior, right?
(2) - Does this dynamic_cast produce undefined behavior if
getFoo() returns a NULL pointer?
If it matters, I'm not using C++11.
Neither are safe and both invoke undefined behavior. C++ doesn't tell
the OS what to do but an operating system exception for accessing memory
at 0 normally occurs in my experience.
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