c++ - 如何使用多个键对 std::set 进行排序

Question

我需要根据多个 key 将一组复制到另一组。键用于 - 共同地 - 维护集合中元素的唯一性和顺序。

我的类(class):

class LaneConnector {
public:

    const Lane* getLaneFrom() const {
        return From;
    }
    const Lane* getLaneTo() const {
        return To;
    }

private:

    Lane* From;
    Lane* To;
}

我的仿函数:

struct MyLaneConectorSorter {
  bool operator() (const LaneConnector* rhs, const LaneConnector* lhs) const
  {

    const Lane* a = lhs->getLaneFrom();
    const Lane* b = rhs->getLaneFrom();

    bool key1 = a->getLaneID() < b->getLaneID();
    bool key2 = a->getLaneParent->ID() < b->getLaneParent->ID();
    bool key2 = a->getLaneParent->getParent->ID() < b->getLaneParent->getParent->ID(); 
    //remind you that I NEED the elements to be in ascending order of 
    //getLaneParent->getParent->ID() ,a->getLaneParent->ID() and then a->getLaneID()
    //duplicate elements are the ones which have all three keys same and need to be discarded 
    return (key1 && key2 && key3); //which dont seem to be working
  }
};

以及我的来源和起源集:

const std::set<LaneConnector*> src = ..... ; //the getter give me a const version
std::set<sim_mob::LaneConnector *, MyLaneConectorSorter> dest;

以及我如何填写:

for(std::set<sim_mob::LaneConnector*>::iterator it = tempLC.begin(); it != tempLC.end(); it++)
{
    dest.insert(*it);//I know I can insert it right at the time of declaration, but keep it like this for now...please 
}

非常感谢您的帮助。

Answer 1

自从获得 operator<对于多个测试，正确是相当困难的，我主张my way of doing this with tuple (在这种情况下使用 make_tuple 而不是 tie 因为我们正在处理从函数返回的临时对象):

#include <tuple>

struct MyLaneConectorSorter {
  bool operator() (const LaneConnector* lhs, const LaneConnector* rhs) const
  {
    const Lane* a = lhs->getLaneFrom();
    const Lane* b = rhs->getLaneFrom();
    auto const* pa = a->getLaneParent();
    auto const* pb = b->getLaneParent();

    return std::make_tuple(a->getLaneID(), pa->ID(), pa->getParent()->ID()) < 
           std::make_tuple(b->getLaneID(), pb->ID(), pb->getParent()->ID())
}

这应该有效，您可以获得 tuple和 make_tuple也来自 Boost，如果您的编译器还没有提供它们的话。