Re: dynamic_cast undefined behavior

From:
Ike Naar <ike@ukato.freeshell.org>
Newsgroups:
comp.lang.c++.moderated
Date:
Sat, 20 Jul 2013 00:23:51 -0700 (PDT)
Message-ID:
<slrn3vfskuk9e9.oc.ike@ukato.freeshell.org>
On 2013-07-20, kawninzx6@googlemail.com <kawninzx6@googlemail.com> wrote:

class BaseFoo
{
  public:
    virtual ~BaseFoo() {}
};

class Foo : public BaseFoo {};

void process(int& i) { ... }

void process(Foo& foo) { ... }

BaseFoo* getFoo() { ... }

int main()
{
  int *i = NULL;
  void process(*i); // (1)

  try
  {
    process(dynamic_cast<Foo&>(*getFoo())); // (2)
  }
  catch (const std::exception&)
  {
    // ignore bad_cast exception
  }

  return 0;
}

(1) - This is always undefined behavior, right?


Yes, dereferencing a null pointer produces undefined behaviour.

(2) - Does this dynamic_cast produce undefined behavior if
      getFoo() returns a NULL pointer?


It's not the dynamic_cast that produces undefined behaviour,
it's the dereference of the null pointer returned by getFoo().

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