Kinds of Iterators

Different algorithms have different requirements for iterators. For example, a find algorithm needs the ++ operator to be defined so the iterator can step through the entire container. It needs read access to data but not write access. (It just looks at data and doesn’t change it.) The usual sorting algorithm, on the other hand, requires random access so that it can swap two non-adjacent elements. If iter is an iterator, you can get random access by defining the + operator so that you can use expressions such as iter + 10. Also a sort algorithm needs to be able to both read and write data.

The STL defines five kinds of iterators and describes its algorithms in terms of which kinds of iterators it needs. The five kinds are the ...

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