[英]How to Use std::unordered_map with std::pair?
我有這個錯誤:
二進制 '==': 'std::pair<const EntityId,EntityData>' 未定義此運算符或轉換為預定義運算符可接受的類型*
在這段代碼中:
using EntityId = unsigned int;
using ComponentContainer = std::vector<C_Base*>;
using EntityData = std::pair<Bitmask,ComponentContainer>;
// ERROR below at line:
using EntityContainer = std::unordered_map<EntityId, EntityData>;
這是C_Base
class:
#include <iostream>
#include <sstream>
#include "ECS_Types.h"
class C_Base{
public:
C_Base(const Component& l_type): m_type(l_type){}
virtual ~C_Base(){}
Component GetType(){ return m_type; }
friend std::stringstream& operator >>(
std::stringstream& l_stream, C_Base& b)
{
b.ReadIn(l_stream);
return l_stream;
}
virtual void ReadIn(std::stringstream& l_stream) = 0;
protected:
Component m_type;
};
以及Bitmask
class:
#include <stdint.h>
using Bitset = uint32_t;
class Bitmask{
public:
Bitmask() : bits(0){}
Bitmask(const Bitset& l_bits) : bits(l_bits){}
Bitset GetMask() const{ return bits; }
void SetMask(const Bitset& l_value){ bits = l_value; }
bool Matches(const Bitmask& l_bits,
const Bitset& l_relevant = 0)const
{
return(l_relevant ?
((l_bits.GetMask() & l_relevant) == (bits & l_relevant))
: (l_bits.GetMask() == bits));
}
bool GetBit(const unsigned int& l_pos)const{
return ((bits&(1 << l_pos)) != 0);
}
void TurnOnBit(const unsigned int& l_pos){
bits |= 1 << l_pos;
}
void TurnOnBits(const Bitset& l_bits){
bits |= l_bits;
}
void ClearBit(const unsigned int& l_pos){
bits &= ~(1 << l_pos);
}
void ToggleBit(const unsigned int& l_pos){
bits ^= 1 << l_pos;
}
void Clear(){ bits = 0; }
private:
Bitset bits;
};
當我嘗試下面的代碼時,我使用 EntityContainer = std::unordered_map;得到這個錯誤 :
'operator __surrogate_func':找不到匹配的重載 function
struct pair_hash {
template <class T1, class T2>
std::size_t operator () ( const std::pair<T1, T2>& p ) const {
auto h1 = std::hash<T1>{}( p.first );
auto h2 = std::hash<T2>{}( p.second );
// Mainly for demonstration purposes, i.e. works but is overly simple
// In the real world, use sth. like boost.hash_combine
return h1 ^ h2;
}
};
using EntityId = unsigned int;
using ComponentContainer = std::vector<C_Base*>;
using EntityData = std::pair<Bitmask,ComponentContainer>;
// ERROR below at line:
using EntityContainer = std::unordered_map<EntityId, EntityData, pair_hash>;
盡管std::pair
實現了operator==
,但它依賴於該pair
的兩個組成部分中的每一個都具有自己的可行operator==
定義(直到 c++20 提供了synthesis_three-way_comparison )。
所以你需要為Bitmask
定義一個相等運算符...
class Bitmask {
public:
...
bool operator== (const Bitmask &other) const
{
return bits == other.bits;
}
};
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