What is the best approach for wrapping an STL container in a custom iterator?

Question

To illustrate, say I have a custom container than makes use of the STL std::vector internally. If I typedef std::vector<char*>::iterator to my_container::iterator , then dereferencing the iterator will return a char* . However, my custom container should hide its internals, meaning I want a dereferencing to return a char .

How can this be accomplished?

class my_container {
public:

    typedef std::vector<char*> vector;

private:

    vector vec_;

};

UPDATE: char* is an example. It does not mean a C string; the example would be clearer with an int .

Also, I would like to use std::forward_iterator_tag and std::iterator as this seems a more standard/current approach.

Answer 1

If you want your own iterator, just start writing it as a nested class. It will need to wrap a std::vector<char*>::iterator , intercepting the usual operations (eg ++ , * , -- ), something like:

class iterator
{
  public:
    iterator& operator++() { ++i_; return *this; }
    char& operator*() { return **i_; }
    ...etc...

  private:
    std::vector<char*>::iterator i_;
};

If you try it and get stuck, post your attempt and we'll help you further.

Answer 2

The best way? phew!, tough question.

one way is to use the very useful framework that has been created for exactly this purpose by the nice folks at boost.org:

http://www.boost.org/doc/libs/1_58_0/libs/iterator/doc/

Answer 3

Use boost::indirect_iterator .

EDIT: (Untested)

struct S
{
    using iterator =
        boost::indirect_iterator<std::vector<char*>::iterator>;
    using const_iterator =
        boost::indirect_iterator<std::vector<char*>::const_iterator>;

    iterator begin() { return iterator(vec_.begin()); }
    iterator end() { return iterator(vec_.begin()); }
    const_iterator begin() const { return const_iterator(vec_.begin()); }
    const_iterator end() const { return const_iterator(vec_.begin()); }
private:
    std::vector<char*> vec_;
};