STL queue iteration

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+3 Q:

STL queue iteration

I need to iterate over a queue. www.cplusplus.com says: By default, if no container class is specified for a particular queue class, the standard container class template deque is used.

So can I somehow get to the queue's underlying deque and iterate over it?

Thanks.

+7 A:

If you need to iterate over a queue then you need something more than a queue. The point of the standard container adapters is to provide a minimal interface. If you need to do iteration as well, why not just use a deque (or list) instead?

Charles Bailey 2009-08-11 08:49:44

While I know what you're saying, I've always disliked this phrasing "something more than a queue". A queue with enumeration is still a queue... Also, observe how `deque` just happens to support enumeration, completely arbitrarily. You could just as well argue that `deque` should be just as purist as `queue` and not support iteration, and if you want to iterate it then you want something "more"; e.g. a `deque_enumerable`. It's a slippery slope though, and my personal feeling is that `queue` should have supported enumeration in the first place.

romkyns 2010-05-31 10:37:42

@romkyns: Would it be better if I rephrased it: "You need something with a richer interface than the `queue` interface so you should choose an object with a suitable interface". Like it or not, iteration isn't part of the `queue` interface so if you want iteration you need to choose something else.

Charles Bailey 2010-05-31 12:28:43

In short: No There is a hack, use vector as underlaid container, so queue::front will return valid reference, convert it to pointer an iterate until <= queue::back

Dewfy 2009-08-11 08:51:37

But you might as well use a vector directly instead...

graham.reeds 2009-08-11 09:04:14

You can also directly use deque - that contains all necessary methods as queue but also supports iteration

Dewfy 2009-08-11 09:16:51

+3 A:

If you need to iterate a queue ... queue isn't the container you need.
Why did you pick a queue?
Why don't you take a container that you can iterate over?

TimW 2009-08-11 08:52:43

I'm not the OP, but here are my answers, in case anyone is curious: 1) I picked a queue because I want a queue. I want to enqueue at one end and dequeue at the other. Is this not a reasonable choice? 2) It's not obvious that a "queue" is not enumerable, nor which structure to use instead. Your answer would have been more helpful if you explained which container to use instead.

romkyns 2010-05-31 10:50:57

ansaurus

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