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Reputation: 107

Can I use pointer arithmetic on pointers to void pointers?

I know you can't utilize pointer arithmetic on void pointers, but could you theoretically do pointer arithmetic on pointers to void pointers, since sizeof(void *) would yield an answer of how many bytes a pointer takes on your system?

Upvotes: 5

Views: 188

Answers (2)

P.W
P.W

Reputation: 26800

Pointer arithmetic is not permitted on void* because void is an incomplete object type.

From C Committee draft N1570:

6.5.6 Additive operators
...
2. For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to a complete object type and the other shall have integer type.

But it is permitted on void** because void* is NOT an incomplete object type. It is like a pointer to a character type.

6.2.5 Types
...
19. The void type comprises an empty set of values; it is an incomplete object type that cannot be completed.
...
28. A pointer to void shall have the same representation and alignment requirements as a pointer to a character type.

Upvotes: 9

Criticize SE actions means ban
Criticize SE actions means ban

Reputation: 58848

Yes, pointer arithmetic works on pointers to void pointers (void**). Only void* is special, void** isn't.

Example:

void *arrayOfVoidPtr[10];
void **second = &arrayOfVoidPtr[1];
void **fifth = second + 3; // pointer arithmetic

Upvotes: 6

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