Question

I’ve got void pointer which I want to do pointer arithmetic on it.
to do so, I want to cast it to a char pointer.

( char * ) buf += current_size;

However when I do so, I get the following error:

error: lvalue required as left operand of assignment

I tried also adding parenthesis on the the whole left side, with no success.
Why do I get this ?

Answer 1

You can avoid the warning by writing the assignment operator out:

buf = (char *)buf + current_size;

Part of the reason you get the warning is that sizeof(void) is undefined and you cannot do arithmetic on void *. Beware: GCC has an extension whereby it treats the code as if sizeof(void) == 1, but that is not in the C standard.

The cast on the LHS of the assignment has no effect on the assignment.