Deque Iterator Error

Question

I have a BinNode<Elem> class for my Binary Search Tree Implementation.

When I initialise the following: deque< BinNode<Elem>* >::const_iterator iter = n.begin(); I get an error telling me that a colon is expected after deque<>.

Does the deque not support a template argument in a template argument or is this some sort of different error?

Here is a snippet of the function:

template <class Key, class Elem, class KEComp, class EEComp>
void BST<Key, Elem, KEComp, EEComp>::
printBranchesHelp(int branchLen, int nodeSpaceLen, int startLen, int nodesInThisLevel, const deque< BinNode<Elem>* >& n, ostream& out)
{
    deque< BinNode<Elem>* >::const_iterator iter = n.begin();
    for (int i = 0; i < nodesInThisLevel / 2; i++) 
    {  
        out << ((i == 0) ? setw(startLen-1) : setw(nodeSpaceLen-2)) << "" << ((*iter++) ? "/" : " ");
        out << setw(2*branchLen+2) << "" << ((*iter++) ? "\\" : " ");
    }
    out << endl;
}

Is `Elem` a template parameter? If so, you might need `typename dequeue< BinNode* >::const_iterator` — TartanLlama, Nov 23 '15 at 10:38
BinNode is the node of the tree, so I am using a pointer to the node which is of type `BinNode` — Kevin Zakka, Nov 23 '15 at 10:40
Please try to create a [Minimal, Complete, and Verifiable Example](http://stackoverflow.com/help/mcve) and show us, and also include the actual (complete and unedited) build log as well. Remember to point out the lines with the error(s) in the MCVE. — Some programmer dude, Nov 23 '15 at 10:40

score 2 · Accepted Answer · edited May 23 '17 at 11:44

2

Since deque< BinNode<Elem>* >::const_iterator is a dependent name, you need to explicitly identify it as a type with the typename keyword:

typename deque< BinNode<Elem>* >::const_iterator iter = n.begin();

You might want to look at this question for a better understanding of dependent names and why you need to use typename.

If you find yourself needing this type a lot, I'd recommend writing an alias or typedef for it:

using deque_iterator = typename deque< BinNode<Elem>* >::const_iterator;

Or in C++11 you could just sidestep the issue and use auto:

auto iter = n.begin();

edited May 23 '17 at 11:44

Community

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answered Nov 23 '15 at 10:41

TartanLlama

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Looking into it, thank you Tartan. (I think you mean deque and not dequeue) – Kevin Zakka Nov 23 '15 at 10:44
Isn't `typename` required just for `Elem` template argument? – Zereges Nov 23 '15 at 10:48
@Zereges the whole name is dependent and could have specializations which expose types or non-types. – TartanLlama Nov 23 '15 at 10:50

Deque Iterator Error

1 Answers1