Expression must be a pointer to a complete object type using simple pointer arithmetic [duplicate]

Question

I'm trying to do some basic pointer arithmetic with a void *. My actual code computes an offset by using sizeof and then multiplying. Here is sample code to show an instance of the issue by itself.

void * p;
p = 0;
p = p + 1;

I'm using the MSVC compiler in C (not C++).

The error is:

expression must be a pointer to a complete object type  

I'm not understanding what this error is trying to say. There is no object or struct here.

Answer 1

Pointer arithmetic is always in terms of the size of the pointed-to object(s). Incrementing a char* will advance the address by one, whereas for int* it would usually be four (bytes). But void has unknown size, so pointer arithmetic on void* is not allowed by the standard. Cast to the appropriate type first; if you just want to manipulate the address as if it were a number then cast to char* or use intptr_t.