Custom iterators, creation

[CornedBee]

As cprogramming.com is (as usual) too slow to be usable, I'll post this stuff here in the hope of inspiring discussion.

The STL and Boost contain a few special standalone iterators. They don't iterator over containers, rather they perform a special function. Those containers are of input_iterator and output_iterator categories and include std::ostream_iterator (wonderful for copying an array to a stream), std::istream_iterator (the reverse), std::back_insert_iterator (append everything to the back of a container) as well as the relatives std::insert_iterator and std::front_insert_iterator and boost::filesystem::directory_iterator (iterate over the files of a directory).

All these iterators aren't obtained by any begin() and end() functions, but created using constructors. For example, an ostream_iterator is created by passing a stream and a separation string:

std::copy(vec.begin(), vec.end(), std::ostream_iterator<std::string>(std::cout, "\n"));

For input iterators (those that can be read from), the "end" iterators are created by passing no arguments to the constructor:

std::vector<int> vec((std::istream_iterator<int>(std::cin)), std::isteam_iterator<int>());

See also Item #6 in Effective STL for the exact syntax of this call.


So far, so good.

I've written three input iterators myself. One iterates over the drives (a:, c:, d:, ...). The second over the network shares (thanks Tech). The third over both by concatenating the two.

The problem is, there isn't anything to initialize. All iterators have system-fixed iteration ranges and thus don't need to be passed any. Right now I have the default constructor creating a start iterator and a static method called end creating the end iterator (via a call to a private constructor that takes a dummy int argument).

However, it doesn't feel quite right. Anybody got a better idea? I want this code to be perfect, I might submit it to Boost.

int index = 1;
for(root_iterator it, end(root_iterator::end()); it != end; ++it) {
	cout << index++ << ": ";
	cout << it->string() << endl;
}

[Technocrat]

Is there anything else that uses iterators in the same fashion? Because you might be able to look at someone elses source to get some ideas.

I think your right, dummy ints doesnt seem like the right thing to do. But I think you are a bit out of my leauge.

You might also try posting this on Codeguru's forums. If you are not a member I would be more than happy to post it for you. There are some really good people in the C++ forums. If no one answers my question here, I usually get it answered there.

[CornedBee]

Do post it, please.

I know of no other code that has such iterators unfortunatly...

[Technocrat]

Ok posted

http://www.codeguru.com/forum/showth...hreadid=272841

I will keep my eye on the email and let you know when there is a response.

[CornedBee]

Never mind, I'll post it myself, just joined.

Oh, you already did.

[Technocrat]

Do you want me to delete it?

[CornedBee]

Nah, leave it there.

[Technocrat]

Someone posted a response at codeguru