Boost Multi-Index 中的上限

Question

我正在尝试学习如何使用 Boost 的多索引，并且我一直在专门查看 http://www.boost.org/doc/libs/1_39_0/libs/multi_index/example/basic.cpp 的基本示例。我如何修改它以仅返回年龄小于特定数字（或 id 等）的员工？

相关代码：

/* Boost.MultiIndex basic example.
 *
 * Copyright 2003-2008 Joaquin M Lopez Munoz.
 * Distributed under the Boost Software License, Version 1.0.
 * (See accompanying file LICENSE_1_0.txt or copy at
 * http://www.boost.org/LICENSE_1_0.txt)
 *
 * See http://www.boost.org/libs/multi_index for library home page.
 */

#if !defined(NDEBUG)
#define BOOST_MULTI_INDEX_ENABLE_INVARIANT_CHECKING
#define BOOST_MULTI_INDEX_ENABLE_SAFE_MODE
#endif

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>

using boost::multi_index_container;
using namespace boost::multi_index;

/* an employee record holds its ID, name and age */

struct employee
{
  int         id;
  std::string name;
  int         age;

  employee(int id_,std::string name_,int age_):id(id_),name(name_),age(age_){}

  friend std::ostream& operator<<(std::ostream& os,const employee& e)
  {
    os<<e.id<<" "<<e.name<<" "<<e.age<<std::endl;
    return os;
  }
};

/* tags for accessing the corresponding indices of employee_set */

struct id{};
struct name{};
struct age{};

/* see Compiler specifics: Use of member_offset for info on
 * BOOST_MULTI_INDEX_MEMBER
 */

/* Define a multi_index_container of employees with following indices:
 *   - a unique index sorted by employee::int,
 *   - a non-unique index sorted by employee::name,
 *   - a non-unique index sorted by employee::age.
 */

typedef multi_index_container<
  employee,
  indexed_by<
    ordered_unique<
      tag<id>,  BOOST_MULTI_INDEX_MEMBER(employee,int,id)>,
    ordered_non_unique<
      tag<name>,BOOST_MULTI_INDEX_MEMBER(employee,std::string,name)>,
    ordered_non_unique<
      tag<age>, BOOST_MULTI_INDEX_MEMBER(employee,int,age)> >
> employee_set;

template<typename Tag,typename MultiIndexContainer>
void print_out_by(
 const MultiIndexContainer& s,
 Tag* =0 /* fixes a MSVC++ 6.0 bug with implicit template function parms */
)
{
  /* obtain a reference to the index tagged by Tag */

  const typename boost::multi_index::index<MultiIndexContainer,Tag>::type& i=
    get<Tag>(s);

  typedef typename MultiIndexContainer::value_type value_type;

  /* dump the elements of the index to cout */

  std::copy(i.begin(),i.end(),std::ostream_iterator<value_type>(std::cout));
}


int main()
{
  employee_set es;

  es.insert(employee(0,"Joe",31));
  es.insert(employee(1,"Robert",27));
  es.insert(employee(2,"John",40));

  /* next insertion will fail, as there is an employee with
   * the same ID
   */

  es.insert(employee(2,"Aristotle",2387));

  es.insert(employee(3,"Albert",20));
  es.insert(employee(4,"John",57));

  /* list the employees sorted by ID, name and age */

  std::cout<<"by ID"<<std::endl;
  print_out_by<id>(es);
  std::cout<<std::endl;

  std::cout<<"by name"<<std::endl;
  print_out_by<name>(es);
  std::cout<<std::endl;

  std::cout<<"by age"<<std::endl;
  print_out_by<age>(es);
  std::cout<<std::endl;

  return 0;
}

Answer 1

您可以在要查询的有序索引上使用上界（或下界，具体取决于您的要求）：

auto const& by_age = get<age>(es);
auto upper = by_age.upper_bound(32);

比如下面的循环

for (auto& e : boost::make_iterator_range(by_age.begin(), upper))
    std::cout << e.name << " is " << e.age << " years old\n";

打印

Albert is 20 years old
Robert is 27 years old
Joe is 31 years old

看Live On Coliru

---

完整代码供参考：

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/range/iterator_range.hpp>
#include <iostream>

using boost::multi_index_container;
using namespace boost::multi_index;

struct employee {
    int         id;
    std::string name;
    int         age;

    friend std::ostream& operator<<(std::ostream& os,const employee& e) {
        return os << e.id << " " << e.name << " " << e.age << std::endl;
    }
};

typedef multi_index_container<
  employee,
  indexed_by<
    ordered_unique<tag<struct id>      , BOOST_MULTI_INDEX_MEMBER(employee, int        , id)>   ,
    ordered_non_unique<tag<struct name>, BOOST_MULTI_INDEX_MEMBER(employee, std::string, name)> ,
    ordered_non_unique<tag<struct age> , BOOST_MULTI_INDEX_MEMBER(employee, int        , age)> >
> employee_set;

int main()
{
    employee_set es;

    es.insert(employee{ 0,       "Joe",   31 });
    es.insert(employee{ 1,    "Robert",   27 });
    es.insert(employee{ 2,      "John",   40 });
    // next insertion will fail, as there is an employee with the same ID
    es.insert(employee{ 2, "Aristotle", 2387 });
    es.insert(employee{ 3,    "Albert",   20 });
    es.insert(employee{ 4,      "John",   57 });

    auto const& by_age = get<age>(es);
    auto upper = by_age.upper_bound(32);

    for (auto& e : boost::make_iterator_range(by_age.begin(), upper))
        std::cout << e.name << " is " << e.age << " years old\n";
}