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To answer one specific part of the question: Does this have anything to do with some systems allowing a different representation of the null pointer other than zero? Sort of. A null pointer ...
Answer
#1: Initial revision
by
Martin Bonner
·
2020-12-08T19:11:07Z (almost 4 years ago)
To answer one specific part of the question: > Does this have anything to do with some systems allowing a different representation of the null pointer other than zero? Sort of. A null pointer constant is zero or zero cast to a `void *`, but that doesn't mean that a null pointer is necessarily represented by "all bits zero". If a null pointer is not "all bits zero", a compiler is obliged to recognize when it is being asked to assign a null pointer constant to a pointer variable, and assign the correct value. Similarly for comparisons. (I have actually used a machine where a null pointer was not "all bits zero" - Prime eventually gave up and added an instruction "is pointer C null" which meant "all bits zero or proper null pointer".)