Can I do arithmetic on void * pointers in C?

Question

is this valid

void *p = &X; /* some thing */
p += 12;

and if so what does p now point to? I have (third party) code that does this (an

Answer 1

I don't think you can, because it doesn't know its type, therefore can not seek the correct amount of bytes.

Cast it to a type first, i.e. (int).