[ethan_g]

No the gp is correct, references in c++ can't be null. Your code invoked undefined behavior before you did anything with a reference, namely *a which is a null pointer dereference.

[the_why_of_y]

> namely *a which is a null pointer dereference.

Which is a textbook example of the null reference problem.

Edit: There may be some terminological confusion here: when programming language folks talk about "references", they include in that definition what C/C++ call "pointers". See for example the Wikipedia article, which gives as the C++ example not C++ references, but C++ pointers.

https://en.wikipedia.org/wiki/Reference_(computer_science)

[mdpopescu]

The "null problem" is that a static language does a run-time check instead of a compile-time check. By the time the undefined behavior is invoked, compilation ended.

[coldtea]

>Your code invoked undefined behavior before you did anything with a reference

Since nobody stopped you, the problem is still there.