A plethora of iterators

As mentioned earlier an iterator is an abstraction that allows code to be generic, that is, to work with different types of containers without knowing the underlying structure of those containers. Most containers support iterators . You can always say:

to produce the types of the iterators produced by that container. Every container has a begin( ) member function that produces an iterator indicating the beginning of the elements in the container, and an end( ) member function that produces an iterator which is the as the past-the-end marker of the container. If the container is const? begin( ) and end( ) produce const iterators, which disallow changing the elements pointed to (because the appropriate operators are const).

All iterators can advance within their sequence (via operator++) and allow == and != comparisons. Thus, to move an iterator it forward without running it off the end, you say something like:

in which pastEnd is the past-the-end marker produced by the container?s end( ) member function.
An iterator can be used to produce the element that it is currently selecting within a container through the dereferencing operator (operator*). This can take two forms. If it is an iterator and f( ) is a member function of the objects held in the container that the iterator is pointing within, you can say either:

(*it).f();

or

it->f();

Knowing this, you can create a template that works with any container. Here, the apply( ) function template calls a member function for every object in the container, using a pointer to member that is passed as an argument:

You can?t use operator-> in this case, because the resulting statement would be
(it->*f)();

which attempts to use the iterator?s operator->*, which is not provided by the iterator classes .
It is much easier to use either for_each( ) or transform( ) to apply functions to sequences anyway.

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