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by j1elo 79 days ago
A nitpick to your nitpick: they said "memory location". And yes, a pointer always points to a memory location. Notwithstanding that each particular region of memory locations could be mapped either to real physical memory or any other assortment of hardware.
2 comments
peterfirefly 79 days ago
No. Neither in the language (NULL exists) nor necessarily on real CPUs.
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bluGill 79 days ago
NULL exists on real CPUs. Maybe you meant nullptr which is a very different thing, don't confuse the two.
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tialaramex 79 days ago
I don't agree. Null is an artefact of the type system and the type system evaporates at runtime. Even C's NULL macro just expands to zero which is defined in the type system as the null pointer.

Address zero exists in the CPU, but that's not the null pointer, that's an embarrassment if you happen to need to talk about address zero in a language where that has the same spelling as a null pointer because you can't say what you meant.

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bluGill 79 days ago
Null doesn't expand to zero on some weird systems. tese days zero is special on most hardware so having zero and nullptr be the same is importnt - even though on some of them zero is also legal.
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tialaramex 78 days ago
Historically C's null pointer literal, provided as the pre-processor constant NULL, is the integer literal 0 (optionally cast to a void pointer in newer standards) even though the hardware representation may not be the zero address.

It's OK that you didn't know this if you mostly write C++ and somewhat OK that you didn't know this even if you mostly write C but stick to pre-defined stuff like that NULL constant, if you write important tools in or for C this was a pretty important gap in your understanding.

In C23 the committee gave C the C++ nullptr constant, and the associated nullptr_t type, and basically rewrote history to make this entire mess, in reality the fault of C++ now "because it's for compatibility with C". This is a pretty routine outcome, you can see that WG14 members who are sick of this tend to just walk away from the committee because fighting it is largely futile and they could just retire and write in C89 or even K&R C without thinking about Bjarne at all.

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kevin_thibedeau 79 days ago
You can point to a register which is certainly not memory.
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