CODEWITHSUNDEEP
c++pointers
huseyin tugrul buyukisik
huseyin tugrul buyukisik

Reputation: 11926

Confusing pointer

When i use the spiral rule, i am confused at below line within 10 spiral steps. Is there a quicker way?

// compiles in VC++ 2010
const void * const ** const volatile ***  const **** _foo_;

Such as ptr is a pointer to a pointer to a pointer to a pointer and all of them are const void but 2 of them are volatile void const

Upvotes: 0

Views: 378

Answers (4)

Paul R
Paul R

Reputation: 213160

cdecl says:

const void * const ** const volatile ***  const **** p

declare p as pointer to pointer to pointer to pointer to const pointer to pointer to pointer to const volatile pointer to pointer to const pointer to const void

Upvotes: 13

jrok
jrok

Reputation: 55425

This is easy with spiral rule!

enter image description here

:-P

Upvotes: 8

Mike Seymour
Mike Seymour

Reputation: 254711

With pointer and reference declarations, you just read from right to left:

ptr is a pointer to a pointer to a pointer to a pointer to a const pointer to a pointer to a pointer to a pointer to a const volatile pointer to a pointer to a const pointer to a const object of unknown type.

If you follow the guideline of putting any const or volatile qualifiers after the first type specifier (i.e. void const *) rather then before it (i.e const void *), then you can read consistently from right to left; otherwise, you sometimes have a slight hiccough when you reach the left-hand end.

The spiral "rule" is occasionally useful for declarations involving arrays or functions, where the name being declared isn't the last thing in the declaration. In this case, with nothing after the name, it degenerates to reading right-to-left.

Upvotes: 7

James Kanze
James Kanze

Reputation: 154017

That's because there is no spiral rule. Basically, you process operands on right first, then on the left, working outward in both cases, and respecting parentheses. And cv-qualifiers normally qualify what's to the left of them. Since this declaration has no operands on the right, it's simply right to left: pointer to pointer to pointer to pointer to const pointer to pointer to pointer to const volatile pointer to pointer to const pointer to (const) void. The last const is because the final const doesn't have anything to the left, so we have to treat the declaration as if it were void const, instead of const void. Other than that, the declaration should cause no problems, if you forget about the misguided spirals.

Upvotes: 5

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