如何使用基于范围的循环语法遍历 STL 容器中的连续对?

Do not modify or copy objects in the container.

推荐答案

这就是我要做的.

#include <iterator>
#include <utility>

template <typename FwdIt> class adjacent_iterator {
public:
    adjacent_iterator(FwdIt first, FwdIt last)
        : m_first(first), m_next(first == last ? first : std::next(first)) { }

    bool operator!=(const adjacent_iterator& other) const {
        return m_next != other.m_next; // NOT m_first!
    }

    adjacent_iterator& operator++() {
        ++m_first;
        ++m_next;
        return *this;
    }

    typedef typename std::iterator_traits<FwdIt>::reference Ref;
    typedef std::pair<Ref, Ref> Pair;

    Pair operator*() const {
        return Pair(*m_first, *m_next); // NOT std::make_pair()!
    }

private:
    FwdIt m_first;
    FwdIt m_next;
};

template <typename FwdIt> class adjacent_range {
public:
    adjacent_range(FwdIt first, FwdIt last)
        : m_first(first), m_last(last) { }

    adjacent_iterator<FwdIt> begin() const {
        return adjacent_iterator<FwdIt>(m_first, m_last);
    }

    adjacent_iterator<FwdIt> end() const {
        return adjacent_iterator<FwdIt>(m_last, m_last);
    }

private:
    FwdIt m_first;
    FwdIt m_last;
};

template <typename C> auto make_adjacent_range(C& c) -> adjacent_range<decltype(c.begin())> {
    return adjacent_range<decltype(c.begin())>(c.begin(), c.end());
}

#include <iostream>
#include <vector>
using namespace std;

void test(const vector<int>& v) {
    cout << "[ ";

    for (const auto& p : make_adjacent_range(v)) {
        cout << p.first << "/" << p.second << " ";
    }

    cout << "]" << endl;
}

int main() {
    test({});
    test({11});
    test({22, 33});
    test({44, 55, 66});
    test({10, 20, 30, 40});
}

打印出来:

[ ]
[ ]
[ 22/33 ]
[ 44/55 55/66 ]
[ 10/20 20/30 30/40 ]

注意事项:

• 我没有对此进行详尽的测试，但它尊重前向迭代器(因为它不会尝试使用 ++、!= 和 * 之外的操作).