c – Boost.MultiIndex：使用多个字段搜索元素

我正在使用Boost multi_index容器来根据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(对于K2和值Y),但我正在寻找一种方法获得满足K1 == X和K2 == Y的所有元素的迭代器.一个明显的解决方案是在满足K1 == X的所有元素上获得迭代器,然后使用谓词K2 == Y构建boost :: filter_iterator,但有没有办法(Bohor.MultiIndex)可以做到这一点(可能更有效)？

谢谢

马蒂厄

解决方法

您可以将 boost::multi_index::composite_key与K1和K2一起使用.

这是一个小例子,也是在ideone.com：

#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>,&Stuff::m_iSecond> >,boost::multi_index::ordered_non_unique<boost::multi_index::tag<BothIdx>,boost::multi_index::composite_key<Stuff,&Stuff::m_iFirst>,&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;
}

原文地址：https://www.jb51.cc/c/119439.html