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

In the early days, programmers were spending lot of time tracing down memory corruption bugs. One day a light bulb light up in some smart programmer's head. He said "What if I make it illegal to access the first page of memory and point all invalid pointers to it?" Once that happened, most memory corruption bugs were quickly found.

That's the history behind null pointer. I heard the story so many years ago, I can't recall any detail now, but I'm sure someone how's older...I mean wiser can tell us more about it.