Question

I want to check to see whether something is null, e.g.:

string xxx(const NotMyClass& obj) {
  if (obj == NULL) {
     //...
  }
}

But the compiler complains about this: there are 5 possible overloads of ==.

So I tried this:

  if (obj == static_cast<NotMyClass>(NULL)) {

This crashes because NotMyClass‘s == overload doesn’t handle nulls.

edit: for everyone tell me it can’t be NULL, I’m certainly getting something NULL like in my debugger:

Answer 1

In a well-formed C++ program, references are never NULL (more accurately, the address of an object to which you have a reference may never be NULL).

So not only is the answer “no, there’s no way”, a corollary is “this makes no sense”.

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Your statement regarding C makes no sense either, since C does not have references.

And as for Java, its “references” are more like C++ pointers in many ways, including this one.

Comparing such specific behaviours between different languages is something of a fool’s errand.

---

If you need this “optional object” behaviour, then you’re looking for pointers:

std::string xxx(const NotMyClass* ptr) {
  if (ptr == NULL)
     throw SomeException();

  const NotMyClass& ref = *ptr;
  /* ... */
}

But consider whether you really need this; a decent alternative might be boost::optional if you really do.