Question

I am writing an iterator for a container which is being used in place of a STL container. Currently the STL container is being used in many places with the c++11 foreach syntax eg: for(auto &x: C). We have needed to update the code to use a custom class that wraps the STL container:

template< typename Type>
class SomeSortedContainer{
    std::vector<typename Type> m_data; //we wish to iterate over this
    //container implementation code
};    
class SomeSortedContainerIterator{
    //iterator code
};

How do I get auto to use the correct iterator for the custom container so the code is able to be called in the following way?:

SomeSortedContainer C;
for(auto &x : C){
    //do something with x... 
}

In general what is required to ensure that auto uses the correct iterator for a class?

Answer 1

You have two choices:

• you provide member functions named begin and end that can be called like C.begin() and C.end();
• otherwise, you provide free functions named begin and end that can be found using argument-dependent lookup, or in namespace std, and can be called like begin(C) and end(C).