std::input_iterator_tag, std::output_iterator_tag, std::forward_iterator_tag, std::bidirectional_iterator_tag, std::random_access_iterator_tag

Original:

The empty types std::input_iterator_tag, std::output_iterator_tag, forward_iterator_tag, bidirectional_iterator_tag, and random_access_iterator_tag are used to select appropriate algorithms based on the category of an iterator. For every iterator type, a typedef std::iterator_traits<Iterator>::iterator_category is available, which is an alias to one of these five tag types.

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Técnica comum para a seleção algoritmo baseado em tags categoria iterador é usar uma função de despachante (a alternativa é std :: enable_if)

#include <iostream>
#include <vector>
#include <list>
#include <iterator>

template< class BDIter >
void alg(BDIter, BDIter, std::bidirectional_iterator_tag)
{
    std::cout << "alg() called for bidirectional iterator\n";
}

template <class RAIter>
void alg(RAIter, RAIter, std::random_access_iterator_tag)
{
    std::cout << "alg() called for random-access iterator\n";
}

template< class Iter >
void alg(Iter first, Iter last)
{
    alg(first, last,
        typename std::iterator_traits<Iter>::iterator_category());
}

int main()
{
    std::vector<int> v;
    alg(v.begin(), v.end());

    std::list<int> l;
    alg(l.begin(), l.end());

//    std::istreambuf_iterator<char> i1(std::cin), i2;
//    alg(i1, i2); // compile error: no matching function for call
}

alg() called for random-access iterator
alg() called for bidirectional iterator