Re: Null and reference

From:

Thomas Richter <thor@math.tu-berlin.de>

Newsgroups:

comp.lang.c++.moderated

Date:

Wed, 25 Dec 2013 12:58:15 CST

Message-ID:

<l9epu9$pr1$1@news2.informatik.uni-stuttgart.de>

On 12/24/2013 11:19 AM, shaanxxx wrote:

I have following function:
void myfunction (int&a , bool g )
{
    if(g)
    {
        int k = a;
    }
}

int main()
{
     int * ptr = NULL;
     myfunction(*ptr, false);

}

Is passing null to a reference legal?

No.

What standard has to say about
this ?

Undefined behavior. Anything can happen. It might just work, or anything
else may happen. It is not too unlikely that the compiler will
internally just handle references similar to pointers, and then call
"myfunction" with a NULL-pointer as first argument. However, as
references must always be valid and cannot be NULL, any check in the
callee, such as

if (&a == NULL) {

}

might be optimized away because the compiler may simply assume that the
reference is never going to be NULL. You don't have such a test in it,
so as said, it might work. But if it works, it works by accident, not by
intent. For the standard, this is just UB.

Greetings,
    Thomas

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