c++ - boost::multi_index_container 复合键中的 equal_range 与比较运算符
问题描述
我正在尝试从值类型是三个元素的结构的多索引容器中查询结果。第一个值是给定的,但第二个和第三个必须大于或小于查询参数。
搜索后,我发现必须实现一个自定义密钥提取器,这里的一些链接建议相同,但我无法实现它:
- boost::multi_index 用户定义的键提取器和复合键
- https://www.boost.org/doc/libs/1_62_0/libs/multi_index/test/test_composite_key.cpp
谁能帮我让它工作?
下面是我的结构和多索引实现:
#define RANKFILTERVIEW 0
struct TPQ {
int UID;
int Value;
int Rank;
TPQ():UID(0),Value(0),Rank(0)
{ }
TPQ(int _T, int _V, int _R):UID(_T),Value(_V),Rank(_R)
{ }
};
typedef bip::allocator<
TPQ,bip::managed_shared_memory::segment_manager
> shared_struct_allocator;
typedef bmi::multi_index_container<
TPQ,
bmi::indexed_by<
bmi::ordered_unique<bmi::tag<struct Composite>,
bmi::composite_key<TPQ,
bmi::member<TPQ, int,&TPQ::UID>,
bmi::member<TPQ, int,&TPQ::Value>,
bmi::member<TPQ, int,&TPQ::Rank>
> >
>,
shared_struct_allocator
> Rank_Set;
typedef nth_index<Rank_Set, RANKFILTERVIEW>::type Rank_view;
int main()
{
bip::managed_shared_memory segment(bip::open_only,"RANKSOTRE");
int UID =52478;
std::pair<Rank_Set*, std::size_t> RankOrderRecord=segment.find<Rank_Set>("RANKDATARECORD");
/// Here I want the result as stated below.
auto range = RankOrderRecord.first->get<Composite>().equal_range(boost::make_tuple(UID,_2>500,_3>5));
}
我有一组指令,应忽略排序或重新排列。
解决方案
你几乎明白了。事实上,为了索引,您可以通过部分键查询。由于这些字段是常规整数类型,因此很容易得出一个好的下限和上限:
auto range = boost::make_iterator_range(
view.lower_bound(boost::make_tuple(UID, 501, 6)),
view.lower_bound(boost::make_tuple(UID+1)));
这是一个完整的演示:
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/member.hpp>
#include <boost/multi_index/composite_key.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/interprocess/allocators/allocator.hpp>
#include <boost/interprocess/managed_mapped_file.hpp> // for Coliru
#include <boost/range/iterator_range.hpp>
#include <iostream>
namespace bmi = boost::multi_index;
namespace bip = boost::interprocess;
struct TPQ {
int UID = 0;
int Value = 0;
int Rank = 0;
TPQ() = default;
TPQ(int _T, int _V, int _R) : UID(_T), Value(_V), Rank(_R) {}
};
static inline std::ostream& operator<<(std::ostream& os, TPQ const& tpq) {
return os << "{ UID: " << tpq.UID
<< ", Value: " << tpq.Value
<< ", Rank: " << tpq.Rank << "}";
}
using shared_struct_allocator = bip::allocator<TPQ, bip::managed_mapped_file::segment_manager>;
using Rank_Set = bmi::multi_index_container<
TPQ,
bmi::indexed_by<
bmi::ordered_unique<
bmi::tag<struct RankFilterView>,
bmi::composite_key<TPQ,
bmi::member<TPQ, int, &TPQ::UID>,
bmi::member<TPQ, int, &TPQ::Value>,
bmi::member<TPQ, int, &TPQ::Rank>
>
>
>,
shared_struct_allocator>;
using Rank_view = bmi::index<Rank_Set, RankFilterView>::type;
int main() {
bip::managed_mapped_file segment(bip::open_or_create, "RANKSOTRE", 10*1024);
auto& table = *segment.find_or_construct<Rank_Set>("RANKDATARECORD")(segment.get_segment_manager());
table.insert({
{52478, 501, 6}, // Match!
{52478, 500, 6}, // - Value too small
{52479, 0, 0}, // - UID too high
{52478, 502, 6}, // Match!
{52478, 502, 7}, // Match!
{52478, 501, 5}, // - Rank too small
{52477, 502, 7}, // - UID too small
{52478, 999, 9}, // Match!
});
int UID = 52478;
Rank_view& view = table.get<RankFilterView>();
auto range = boost::make_iterator_range(
view.lower_bound(boost::make_tuple(UID, 501, 6)),
view.upper_bound(UID));
for (TPQ const& tpq : range) {
std::cout << tpq << "\n";
}
}
正如预期的那样,它只会打印:
{ UID: 52478, Value: 501, Rank: 6}
{ UID: 52478, Value: 502, Rank: 6}
{ UID: 52478, Value: 502, Rank: 7}
{ UID: 52478, Value: 999, Rank: 9}
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