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?
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2 Answers
Pointer arithmetic is not permitted on void* because void is an incomplete object type.
From C Committee draft N1570:
6.5.6 Additive operators
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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
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19. The void type comprises an empty set of values; it is an incomplete object type that cannot be completed.
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28. A pointer to void shall have the same representation and alignment requirements as a pointer to a character type.
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
answered Sep 6, 2018 at 2:56
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Some compilers allow as an extension
void * arithmetics. One of the examples is gcc