c++ - 无法使用对类型键设置映射值

Question

#include <vector>
#include <map>
#include <algorithm>
using namespace std;
class NodePoint {
  public:
  int x, y;
  NodePoint (int i, int j){x=i; y=j;}
  NodePoint (){}
  bool operator == (const NodePoint &rhs) { return (x == rhs.x && y == rhs.y); };
  bool operator != (const NodePoint &rhs) { return (x != rhs.x || y != rhs.y); };
};
class Link {
  public:
  Link (){}
};
int main() {
  vector < vector <NodePoint> > nodes;
  map < pair < NodePoint, NodePoint > , Link > node_links;
  int sol_row_size = 10, sol_col_size = 10, i, j;
  for(i=0; i<sol_row_size; i++) {
    vector < NodePoint > tn;
    for(j=0; j<sol_col_size; j++) tn.push_back(NodePoint(i,j));
    nodes.push_back(tn);
  }
  for(i=0; i<sol_row_size; i++) {
    for(j=0; j<(sol_col_size-1); j++) {
      node_links[make_pair(nodes[i][j], nodes[i][j+1])] = Link();
    }
  }
  return 0;
}

在上面的程序中，我只是尝试创建一个名为 node_links 的映射，其键将是一对 2 个输入节点，但我遇到了大量的编译错误(而且毫无意义我的代码中的一些行)而且我不太习惯 cpp，有什么帮助吗？我做错了什么？

编译错误如下:

$ g++ temp.cpp -o temp;
In file included from /usr/include/c++/4.6/bits/stl_algobase.h:65:0,
                 from /usr/include/c++/4.6/vector:61,
                 from temp.cpp:1:
/usr/include/c++/4.6/bits/stl_pair.h: In function ‘bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) [with _T1 = NodePoint, _T2 = NodePoint]’:
/usr/include/c++/4.6/bits/stl_function.h:236:22:   instantiated from ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::pair<NodePoint, NodePoint>]’
/usr/include/c++/4.6/bits/stl_map.h:452:2:   instantiated from ‘std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = std::pair<NodePoint, NodePoint>, _Tp = Link, _Compare = std::less<std::pair<NodePoint, NodePoint> >, _Alloc = std::allocator<std::pair<const std::pair<NodePoint, NodePoint>, Link> >, std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = Link, std::map<_Key, _Tp, _Compare, _Alloc>::key_type = std::pair<NodePoint, NodePoint>]’
temp.cpp:35:55:   instantiated from here
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: no match for ‘operator<’ in ‘__x.std::pair<NodePoint, NodePoint>::second < __y.std::pair<NodePoint, NodePoint>::second’
/usr/include/c++/4.6/bits/stl_pair.h:209:62: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:207:5: note: template<class _T1, class _T2> bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
/usr/include/c++/4.6/bits/stl_iterator.h:291:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:341:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
/usr/include/c++/4.6/bits/stl_vector.h:1290:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
/usr/include/c++/4.6/bits/stl_tree.h:866:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator<(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_map.h:899:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_multimap.h:817:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: no match for ‘operator<’ in ‘__y.std::pair<NodePoint, NodePoint>::first < __x.std::pair<NodePoint, NodePoint>::first’
/usr/include/c++/4.6/bits/stl_pair.h:209:62: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:207:5: note: template<class _T1, class _T2> bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
/usr/include/c++/4.6/bits/stl_iterator.h:291:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:341:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
/usr/include/c++/4.6/bits/stl_vector.h:1290:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
/usr/include/c++/4.6/bits/stl_tree.h:866:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator<(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_map.h:899:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_multimap.h:817:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: no match for ‘operator<’ in ‘__x.std::pair<NodePoint, NodePoint>::first < __y.std::pair<NodePoint, NodePoint>::first’
/usr/include/c++/4.6/bits/stl_pair.h:209:62: note: candidates are:
/usr/include/c++/4.6/bits/stl_pair.h:207:5: note: template<class _T1, class _T2> bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&)
/usr/include/c++/4.6/bits/stl_iterator.h:291:5: note: template<class _Iterator> bool std::operator<(const std::reverse_iterator<_Iterator>&, const std::reverse_iterator<_Iterator>&)
/usr/include/c++/4.6/bits/stl_iterator.h:341:5: note: template<class _IteratorL, class _IteratorR> bool std::operator<(const std::reverse_iterator<_IteratorL>&, const std::reverse_iterator<_IteratorR>&)
/usr/include/c++/4.6/bits/stl_vector.h:1290:5: note: template<class _Tp, class _Alloc> bool std::operator<(const std::vector<_Tp, _Alloc>&, const std::vector<_Tp, _Alloc>&)
/usr/include/c++/4.6/bits/stl_tree.h:866:5: note: template<class _Key, class _Val, class _KeyOfValue, class _Compare, class _Alloc> bool std::operator<(const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&, const std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_map.h:899:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::map<_Key, _Tp, _Compare, _Alloc>&, const std::map<_Key, _Tp, _Compare, _Alloc>&)
/usr/include/c++/4.6/bits/stl_multimap.h:817:5: note: template<class _Key, class _Tp, class _Compare, class _Alloc> bool std::operator<(const std::multimap<_Key, _Tp, _Compare, _Alloc>&, const std::multimap<_Key, _Tp, _Compare, _Alloc>&)

更新 1

我已将以下内容添加到 NodePOint 类

bool operator < (const NodePoint &rhs) {
    return (x < rhs.x || (x == rhs.x && y < rhs.y));
};

我收到以下错误:

In file included from /usr/include/c++/4.6/bits/stl_algobase.h:65:0,
                 from /usr/include/c++/4.6/vector:61,
                 from temp.cpp:1:
/usr/include/c++/4.6/bits/stl_pair.h: In function ‘bool std::operator<(const std::pair<_T1, _T2>&, const std::pair<_T1, _T2>&) [with _T1 = NodePoint, _T2 = NodePoint]’:
/usr/include/c++/4.6/bits/stl_function.h:236:22:   instantiated from ‘bool std::less<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::pair<NodePoint, NodePoint>]’
/usr/include/c++/4.6/bits/stl_map.h:452:2:   instantiated from ‘std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type& std::map<_Key, _Tp, _Compare, _Alloc>::operator[](const key_type&) [with _Key = std::pair<NodePoint, NodePoint>, _Tp = Link, _Compare = std::less<std::pair<NodePoint, NodePoint> >, _Alloc = std::allocator<std::pair<const std::pair<NodePoint, NodePoint>, Link> >, std::map<_Key, _Tp, _Compare, _Alloc>::mapped_type = Link, std::map<_Key, _Tp, _Compare, _Alloc>::key_type = std::pair<NodePoint, NodePoint>]’
temp.cpp:37:55:   instantiated from here
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: passing ‘const NodePoint’ as ‘this’ argument of ‘bool NodePoint::operator<(const NodePoint&)’ discards qualifiers [-fpermissive]
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: passing ‘const NodePoint’ as ‘this’ argument of ‘bool NodePoint::operator<(const NodePoint&)’ discards qualifiers [-fpermissive]
/usr/include/c++/4.6/bits/stl_pair.h:209:62: error: passing ‘const NodePoint’ as ‘this’ argument of ‘bool NodePoint::operator<(const NodePoint&)’ discards qualifiers [-fpermissive]

Answer 1

你需要定义operator<在 NodePoint , 这样您的节点对就可以被排序( std::pair<NodePoint, NodePoint> 自动为您定义 operator< ，根据 NodePoint::operator< )

大概你想要这样的东西:

bool operator <(const NodePoint &rhs) const {
    return (x < rhs.x || (x == rhs.x && y < rhs.y));
};

编辑添加const