Re: Valid C++?
* Kai-Uwe Bux:
Alf P. Steinbach wrote:
* Rolf Magnus:
[snip]
Actually, the exception covers not only typeid, but also sizeof:
"An expression is potentially evaluated unless either it is the operand
of the sizeof operator (5.3.3), or it is the operand of the typeid
operator and does not designate an lvalue of polymorphic class type
(5.2.8)."
No, that isn't the exception that applies to typeid.
And no, it doesn't matter whether a dereferencing is potentially
evaluated or not.
That sounds like a defect. Would you please give chapter and verse on this
one.
The typeid defect is being addressed, but the proposed resolution is to
allow null-pointer dereferencing in general; see typeid.
The nullpointer dereferencing no matter runtime evaluation or not is
because nullpointer dereferencing is stated (twice) as undefined
behavior without reference to runtime or compile time evaluation.
More about that: the para that Rolf Magnus quoted /defines/ the term
"used" as appearing in a potentially evaluated expression, and restricts
it applicability to objects and functions. The nullpointer constant is
not an object, and so it's formally never "used". It's in the same
league as division by zero: compile time or not doesn't matter.
--
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet and in e-mail?
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