In terms of contract in a function, you might be passing the pointer to the function so that the function can write to the provided pointer address. Input/output isn't specifying calling convention (there's fastcall for that) - it is specifying the intent of the function. Otherwise every single parameter to a function would be an input because the function takes it and uses it...
I worked on a massive codebase where we used Microsoft SAL to annotate all parameters to specify intent. The compiler could throw errors based on these annotations to indicate misuse.
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.
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.
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.
I worked on a massive codebase where we used Microsoft SAL to annotate all parameters to specify intent. The compiler could throw errors based on these annotations to indicate misuse.
This seems like an extension of that.