在C++中使用map()时出现错误

Question

我写了一段代码，使用了地图和矢量，但它显示了一些我无法获得的东西。如果有人以这种方式帮助我并更正我的代码或给我一些提示，我将不胜感激。

代码是：

      // For each node in N, calculate the reachability, i.e., the
      // number of nodes in N2 which are not yet covered by at
      // least one node in the MPR set, and which are reachable
      // through this 1-hop neighbor
      std::map<int, std::vector<const NeighborTuple *> > reachability;
      std::set<int> rs;
      for (NeighborSet::iterator it = N.begin(); it != N.end(); it++)
        {
          NeighborTuple const &nb_tuple = *it;
          int r = 0;
          for (TwoHopNeighborSet::iterator it2 = N2.begin (); it2 != N2.end (); it2++)
            {
              TwoHopNeighborTuple const &nb2hop_tuple = *it2;
              if (nb_tuple.neighborMainAddr == nb2hop_tuple.neighborMainAddr)
                r++;
            }
          rs.insert (r);
          reachability[r].push_back (&nb_tuple);
        }
/*******************************************************************************/
//for keepping exposition of a node
        std::map<Vector, std::vector<const NeighborTuple *> > position; 
        std::set<Vector> pos; 
        for (NeighborSet::iterator it = N.begin(); it != N.end(); it++)
        {
          NeighborTuple   nb_tuple = *it;

          Vector exposition;
          pos.insert (exposition);
          position[exposition].push_back (&nb_tuple);
        } 

错误是针对这一行的：position[exposition].push_back (&nb_tuple);，错误是：

/usr/include/c++/4.1.2/bits/stl_function.h: In member function ‘bool std::less<_
Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = ns3::Vector3D]’:
/usr/include/c++/4.1.2/bits/stl_map.h:347:   instantiated from ‘_Tp& std::map<_K
ey, _Tp, _Compare, _Alloc>::operator[](const _Key&) [with _Key = ns3::Vector3D, _Tp = std::vector<const ns3::olsr::NeighborTuple*, std::allocator<const ns3::olsr::NeighborTuple*> >, _Compare = std::less<ns3::Vector3D>, _Alloc = std::allocator<std::pair<const ns3::Vector3D, std::vector<const ns3::olsr::NeighborTuple*, std::allocator<const ns3::olsr::NeighborTuple*> > > >]’
../src/routing/olsr/olsr-routing-protocol.cc:853:   instantiated from here
/usr/include/c++/4.1.2/bits/stl_function.h:227: error: no match for ‘operator<’ in ‘__x < __y’
debug/ns3/ipv6-address.h:432: note: candidates are: bool ns3::operator<(const ns3::Ipv6Address&, const ns3::Ipv6Address&)
debug/ns3/nstime.h:475: note:                 bool ns3::operator<(const ns3::Time&, const ns3::Time&)
debug/ns3/ipv4-address.h:305: note:                 bool ns3::operator<(const ns3::Ipv4Address&, const ns3::Ipv4Address&)
debug/ns3/address.h:231: note:                 bool ns3::operator<(const ns3::Address&, const ns3::Address&)
debug/ns3/type-id.h:376: note:                 bool ns3::operator<(ns3::TypeId, ns3::TypeId)

提前谢谢。巴哈

Answer 1

您声明的position对象如下：std::map<Vector, std::vector<const NeighborTuple *> > position;

你想把NeighborTuple *推进去..。

尝试使用const NeighborTuple *

Answer 2

std::map是对的有序容器。因此，映射中的键必须定义了operator <()。确保Vector定义了小于运算符。

例如：

class Vector {
    int len, ang;
    friend bool operator<(const Vector&, const Vector&);
};

bool operator<(const Vector& v1, const Vector& v2)
{
    return true_if_v1_is_less_than_v2();  // you define what "less than" means
}

当然，还有其他方法可以做到这一点。您可以使operator<成为成员函数。或者，您可以将两个成员数据设置为公共数据，并将运算符设置为非成员、非友元函数。或者，您可以在匿名名称空间中定义operator<，以增强信息隐藏。或者，您可以使用operator<以外的比较器。

Answer 3

我注意到你似乎有一个可以编译的推回行和一个不能编译的推回行。

不同之处可能在于第一种情况下有一个const

NeighborTuple const &nb_tuple = *it;