Question

我正在尝试使用unordered_map将密钥作为一对uint和类Tile的值。

#include <iostream>
#include <unordered_map>
#include <boost/functional/hash.hpp>

class Tile {
public:
  std::pair<uint, uint> coordinate;

  bool operator==(const Tile &t) {
    return this->coordinate.first == t.coordinate.first
      && this->coordinate.second == t.coordinate.second;
  }

  Tile (uint x, uint y) {
    this->coordinate.first = x;
    this->coordinate.second = y;
  }

  std::pair<uint, uint> GetCoor() const 
  {return this->coordinate;}

  uint GetX() const 
  {return coordinate.first;}      

  uint GetY() const 
  {return coordinate.second;}          
};

struct TileHash {
  std::size_t operator()(const Tile &t) const
  {
    size_t seed = 0;
    boost::hash_combine (seed, t.GetX());
    boost::hash_combine (seed, t.GetY());
    return seed;
  }
};

int main ()
{
  std::unordered_map<std::pair<uint, uint>, Tile, TileHash> board;
  Tile t1 = Tile (0, 0);

  board.insert (std::make_pair (t1.GetCoor(), t1));
  //board[t1.GetCoor()] = t1; // This causes a different error at compile time...    
}

我收到以下错误，然后是我未粘贴的一些注释

/usr/include/c++/v1/unordered_map:400:17: error: no matching function for call to object of type 'const TileHash'
        {return static_cast<const _Hash&>(*this)(__x.__cc.first);}
                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/v1/__hash_table:1712:21: note: in instantiation of member function 'std::__1::__unordered_map_hasher<std::__1::pair<unsigned int, unsigned int>, std::__1::__hash_value_type<std::__1::pair<unsigned int, unsigned int>,
      Tile>, TileHash, true>::operator()' requested here
    size_t __hash = hash_function()(__x);
                    ^
/usr/include/c++/v1/__hash_table:1692:12: note: in instantiation of member function 'std::__1::__hash_table<std::__1::__hash_value_type<std::__1::pair<unsigned int, unsigned int>, Tile>,
      std::__1::__unordered_map_hasher<std::__1::pair<unsigned int, unsigned int>, std::__1::__hash_value_type<std::__1::pair<unsigned int, unsigned int>, Tile>, TileHash, true>, std::__1::__unordered_map_equal<std::__1::pair<unsigned
      int, unsigned int>, std::__1::__hash_value_type<std::__1::pair<unsigned int, unsigned int>, Tile>, std::__1::equal_to<std::__1::pair<unsigned int, unsigned int> >, true>,
      std::__1::allocator<std::__1::__hash_value_type<std::__1::pair<unsigned int, unsigned int>, Tile> > >::__insert_unique_value' requested here
    return __insert_unique_value(__x);

我知道我unordered_map的实例化是可以的，当我编译时没有调用插入all就好了。

Answer 1

通过TileHash，你提供了一个const Tile&的哈希函数。

该实现正在寻找一个带const std::pair<uint, uint>&的哈希函数。

那是因为它是被散列的关键，而不是映射值。

所以，你是在做错事。

该标准并没有给我们配对，但Boost确实如此：

std::unordered_map<
   std::pair<uint, uint>,
   Tile,
   boost::hash<std::pair<uint, uint>>
> board;

C ++ unordered_map＆lt; pair <uint，uint =“”>，UserClass＆gt;插入

1 个答案: