Re: Copying singular iterators
Dave Harris wrote:
pete@versatilecoding.com (Pete Becker) wrote (abridged):
Nope, not missing. Iterators aren't just pointers in fancy dress.
They're used in pairs, to designate ranges of elements.
They are also used on their own. For example, std::vector::insert takes a
single iterator which says where the insertion should happen.
Yes, but that's an iterator that was obtained from a range, not one that
was made up on the spot. It's known to be valid, either pointing to an
element in the range or past the end, i.e. no element.
Idiomatic STL (as in Standard Template Library, not C++ STandard
Library) doesn't need a distinguished value for an iterator that
points nowhere.
True, but I've seen user code that wanted one.
That's a design problem in the user code.
And even the STL has one-past-the-end iterators which point to no object.
Which is why I explicitly said "_a_ distinguished value" (emphasis
added). By design, STL does not have such a thing.
These are often usable, but they depend on a particular container.
Not on a container, but on the sequence that they are applied to.
Containers are one way of creating sequences, but not the only one.
Given
the importance of NULL in the C++ memory model, it's a shame iterators
don't support it.
I haven't seen a convincing case for it. All the suggestions I've seen
for having such a thing have come from misunderstanding how STL is
designed. Iterators aren't pointers, and they don't need to act like
them. Applications that need pointer semantics should use pointers.
--
-- Pete
Roundhouse Consulting, Ltd. (www.versatilecoding.com)
Author of "The Standard C++ Library Extensions: a Tutorial and
Reference." (www.petebecker.com/tr1book)
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