Using Iterator in Queue

[Donos]

Hello

I have a Queue which is declared as,

std::queue<unsigned char> m_Queue;

I push data into this queue.

Now i want to take the data out of this queue using Iterator.

I tried declaring the Iterator as,

std::iterator<unsigned char> m_Itr;

But it's not working.

Can anyone tell me how to declare an Iterator and take data out of a
Queue?

Thanks.

 

[Markus Moll]

Hi

I have a Queue which is declared as,

std::queue<unsigned char> m_Queue;

I push data into this queue.

Now i want to take the data out of this queue using Iterator.

std::queue is not itself a container, but an adaptor (a facade) around a
container offering a limited interface. As such, std::queue does not offer
iterators.

I tried declaring the Iterator as,

std::iterator<unsigned char> m_Itr;

There is a std::iterator template, but it does not do what you think it
does. Furthermore, iterators are not runtime-polymorphic, so there cannot
be a general iterator class for arbitrary containers. Instead, the iterator
class is always tightly bound to the corresponding container class. E.g.

But it's not working.

No, it shouldn't.

Can anyone tell me how to declare an Iterator and take data out of a
Queue?

No way. If you want to iterate over the queue, you do not want a std::queue
but rather one of the containers that allow addition and removal at both
ends. Those would be std::list and std::deque.

Markus

 

[Donos]

But still i can use a Queue to push data into it, right?
ie; std::queue<unsigned char> m_Queue;

I tried declaring the Iterator as ,

std::deque<unsigned char>::iterator m_Itr;
then,

m_Itr = m_Queue.front(); // ERROR C2679

And this gives an error.

error C2679: binary '=' : no operator found which takes a right-hand
operand of type 'unsigned char' (or there is no acceptable conversion)

Any idea?

 

[Markus Moll]

Hi

But still i can use a Queue to push data into it, right?

I don't quite understand...

ie; std::queue<unsigned char> m_Queue;

This looks good.

I tried declaring the Iterator as ,

std::deque<unsigned char>::iterator m_Itr;
then,

m_Itr = m_Queue.front(); // ERROR C2679

front() returns the first element, not an iterator to the first element. The
latter is returned by begin(). So it should read:

std::deque<unsigned char>::iterator m_Itr = m_Queue.begin();

Markus

 

[Donos]

But still i can use a Queue to push data into it, right?
ie; std::queue<unsigned char> m_Queue;

I tried declaring the Iterator as ,

std::deque<unsigned char>::iterator m_Itr;
then,

m_Itr = m_Queue.front(); // ERROR C2679

And this gives an error.

error C2679: binary '=' : no operator found which takes a right-hand
operand of type 'unsigned char' (or there is no acceptable conversion)

Any idea?

 

[Rolf Magnus]

But still i can use a Queue to push data into it, right?

Yes, that's what queues are for. There is just no need to use an iterator
for that.

 

[Guest]

But still i can use a Queue to push data into it, right?
ie; std::queue<unsigned char> m_Queue;

If you can live with not having any iterators to its elements and want
to use it just like a queue then it is perfect for the job.

 

[James Kanze]

But still i can use a Queue to push data into it, right?
ie; std::queue<unsigned char> m_Queue;

I tried declaring the Iterator as ,

std::deque<unsigned char>::iterator m_Itr;
Why?


m_Itr = m_Queue.front(); // ERROR C2679

And this gives an error.

error C2679: binary '=' : no operator found which takes a right-hand
operand of type 'unsigned char' (or there is no acceptable conversion)

Queues are meant for queueing, not iterating. You can't get an
iterator into a queue, and if you need one, you shouldn't be
using a queue. And since there are no iterators for a queue,
you can't declare one.

What's wrong with simply:

unsigned char ch = m_Queue.front() ;

?