What part of dereferencing NULL pointers causes undesired behavior?

Question

I am curious as to what part of the dereferencing a NULL ptr causes undesired behavior. Example:

//  #1
someObj * a;
a = NULL;
(*a).somefunc();   // crash, dere         


        

Answer 1

Tom's comment is correct, I did not initialize correctly therefore the question is ambiguous at best yet most everyone directly answered my question, I unwittingly submitted the question while not logged in (sorry I'm new to stackoverflow) so can someone with editing powers update the OP?

//  #2
someObj * b;
anotherObj * c = new anotherObj();        //initialize c
b = NULL;
c->anotherfunc(*b);   // *b is in question not the c dereference