Question

Is it possible to initialize a reference member to NULL in c++?
I’m trying to something like this:

class BigClass
{
private:
    Object m_inner;
public:
    const Object& ReadOnly;
    BigClass() : ReadOnly(NULL)
    {
      Do stuff.
    }
};

I know I can do this if I initialize "ReadOnly" to a real reference of an object, but when I want to put in there "NULL", i get the error:

"cannot convert from ‘int’ to ‘const Object &’

How can I solve this?

Answer 1

No, references cannot be NULL in C++.¹

Possible solutions include:

• using a pointer instead of a reference.
• having a dummy Object instance that can be used to indicate “no object”.

---

_{[1] From the C++11 standard:}

_{[dcl.ref] […] a null reference cannot exist in a well-defined program, because the only way to create such a reference would be to bind it to the “object” obtained by dereferencing a null pointer, which causes undefined behavior.}