Messages in this thread | | | Subject | Re: [PATCH] C undefined behavior fix | From | Florian Weimer <> | Date | Sat, 05 Jan 2002 21:01:11 +0100 |
| |
jkl@miacid.net writes:
> An arbitrary integer may be converted to a pointer. > ^^^^^^^^^
This rule exists so that implementations are not forced to issue a diagnostic for (char *)1.
> I interpret this to mean that one MAY use integer arithmatic to > do move a pointer outside the bounds of an array. Specifically, as soon > as I've cast the pointer to an integer, the compiler has an obligation to > forget any assumptions it makes about that pointer. This is what casts > from pointer to integer are for! when i say (int)p I'm saying that I > understand the address structure of the machine and I want to manipulate > the address directly.
According to the standard, you say that you want to cast p to type int. You cannot manipulate machine addresses in C because C is defined as a high-level language, without backdoors to such low-level concepts as machine addresses.
The fact that quite a few implementations traditionally provide such backdoors in some cases does not mean that the C language is a low-level language, or that all implementations (even future ones) have to provide these backdoors.
> If the satandard has changed so this is no longer possible, there > NEEDS to be some other way in the new standard to express the same > concept, or large application domains where C is currently in use will > stop working.
I don't think there are fundamental and conceptual changes in C99 in this area. Even with previous C reversions, you should have read the compiler manual carefully before doing address arithmetic. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |