Boost.MultiIndex：使用多个字段搜索元素

Question

我使用 Boost multi_index 容器根据 2 个整数键 K1 和 K2 存储对象。我可以轻松地检索满足“K1 == X”的所有元素的迭代器，例如，通过获取第一个索引并使用 find() 函数（同上 K2 和值 Y），但我正在寻找一种方法获取满足 K1 == X 和 K2 == Y 的所有元素的迭代器。一个明显的解决方案是获取满足 K1 == X 的所有元素的迭代器，然后使用谓词 K2 == Y 构建 boost::filter_iterator，但有吗一种只能从 Boost.MultiIndex 做到这一点的方法（也许更有效）？

谢谢马蒂厄

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Answer 1

您可以使用 boost::multi_index::composite_key 同时具有 K1 和 K2。

这是一个小例子，也在 ideone.com 上：

#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/composite_key.hpp>

#include <iostream>

struct Stuff
{
    Stuff (int iFirst, int iSecond)
        : m_iFirst(iFirst),
          m_iSecond(iSecond)
    {
    }

    int m_iFirst;
    int m_iSecond;

};

std::ostream& operator<<(std::ostream& rOut, Stuff const& rStuff)
{
    return rOut << rStuff.m_iFirst << "/" << rStuff.m_iSecond << "\n";
}


struct FirstIdx{};
struct SecondIdx{};
struct BothIdx{};

typedef boost::multi_index_container<
    Stuff,
    boost::multi_index::indexed_by<
        boost::multi_index::ordered_non_unique<boost::multi_index::tag<FirstIdx>, boost::multi_index::member<Stuff, int, &Stuff::m_iFirst> >,
        boost::multi_index::ordered_non_unique<boost::multi_index::tag<SecondIdx>, boost::multi_index::member<Stuff, int, &Stuff::m_iSecond> >,
        boost::multi_index::ordered_non_unique<boost::multi_index::tag<BothIdx>, boost::multi_index::composite_key<Stuff, boost::multi_index::member<Stuff, int, &Stuff::m_iFirst>,
                                                                                                                          boost::multi_index::member<Stuff, int, &Stuff::m_iSecond> > >
        >
    > TDicStuffs;

typedef TDicStuffs::index<FirstIdx>::type TFirstIdx;
typedef TDicStuffs::index<SecondIdx>::type TSecondIdx;
typedef TDicStuffs::index<BothIdx>::type TBothIdx;

int main(int argc, char *argv[])
{

    TDicStuffs stuffs;

    // fill some stuffs
    stuffs.insert(Stuff(1, 1));
    stuffs.insert(Stuff(1, 2));
    stuffs.insert(Stuff(1, 3));
    stuffs.insert(Stuff(2, 1));
    stuffs.insert(Stuff(2, 2));
    stuffs.insert(Stuff(2, 3));
    stuffs.insert(Stuff(3, 1));
    stuffs.insert(Stuff(3, 2));
    stuffs.insert(Stuff(3, 3));

    assert(stuffs.size() == 9);

    // search for m_iFirst == 2
    TFirstIdx::const_iterator itFirstLower;
    TFirstIdx::const_iterator itFirstUpper;

    boost::tie(itFirstLower, itFirstUpper) = stuffs.get<FirstIdx>().equal_range(2);

    assert(std::distance(itFirstLower, itFirstUpper) == 3);

    std::copy(itFirstLower, itFirstUpper, std::ostream_iterator<Stuff>(std::cout << "\n")); 

    // search for m_iSecond == 3
    TSecondIdx::const_iterator itSecondLower;
    TSecondIdx::const_iterator itSecondUpper;

    boost::tie(itSecondLower, itSecondUpper) = stuffs.get<SecondIdx>().equal_range(3);

    assert(std::distance(itSecondLower, itSecondUpper) == 3);

    std::copy(itSecondLower, itSecondUpper, std::ostream_iterator<Stuff>(std::cout << "\n")); 

    // search for m_iFirst == 2 m_iSecond == 3
    TBothIdx::const_iterator itBothLower;
    TBothIdx::const_iterator itBothUpper;

    boost::tie(itBothLower, itBothUpper) = stuffs.get<BothIdx>().equal_range(boost::make_tuple(2,3));

    assert(std::distance(itBothLower, itBothUpper) == 1);

    std::copy(itBothLower, itBothUpper, std::ostream_iterator<Stuff>(std::cout << "\n")); 

    return 0;
}