Why convert to pointer type before added to a pointer

[Jie Zhang]

Hi Jeff,

> 
> It's an unfortunate aspect of the type system we have -- basically
> both operands of a binary operator need to have compatible types.
>

Why does our type system behave like this? Could you or somebody else 
give me an outline of the type system?

> 
> The first approach is to have a separate set of operators such as
> PLUS_PTR_EXPR, MINUS_PTR_EXPR which do not require their operands
> to be the same type.  That's ugly simply because everywhere you 
> generate or test for PLUS_EXPR or MINUS_EXPR you have to to examine
> the types to determine instead you should be using PLUS_PTR_EXPR
> or MINUS_PTR_EXPR.
> 
> The other approach is to relax the type system.  That's bad from the
> standpoint of being able to perform internal consistency checking.
> 
I think the latter one is better. I would even say it's to correct the 
type system. In the C99 standard, it reads

   6.5.6.2
   For addition, either both operands shall have arithmetic type,
   or one operand shall be a pointer to an object type and the
   other shall have integer type.

Adding two pointers is not allowed by the constraints. But I may miss 
something, since I now have little knowledge on our type system.


cheers
-- 
Jie