Is (int *)0 a null pointer?

Question

This could be thought of as an extension to this question (I\'m interested in C only, but adding C++ to complete the extension)

The C11 standard at 6.3.2.3.3 says:

Answer 1

Evaluating the expression (int*)0 yields a null pointer of type int*.

(int*)0 is not a null pointer constant.

A null pointer constant is a particular kind of expression that may appear in C source code. A null pointer is a value that may occur in a running program.

C and C++ (being two distinct languages) have slightly different rules in this area. C++ doesn't have the "or such an expression cast to type void*" wording. But I don't think that affects the answer to your question.

As for your question about (long long)123, I'm not sure how it's related, but the expression 123 is of type int, and the cast specifies a conversion from int to long long.

I think the core confusion is an assumption that the cast in (int*)0 does not specify a conversion, since 0 is already a null pointer constant. But a null pointer constant is not necessarily an expression of pointer type. In particular, the expression 0 is both a null pointer constant and an expression of type int; it is not of any pointer type. The term null pointer constant needs to be thought of as a single concept, not a phrase whose meaning depends on the individual words that make it up.