如何在 std::map 中使用结构作为键 [英] How to use struct as key in std::map

问题描述

我想使用一个 std::map，它的键和值元素是结构.

I want to use a std::map whose key and value elements are structures.

我收到以下错误:error C2784: 'bool std::operator <(const std::basic_string<_Elem,_Traits,_Alloc> &,const _Elem *)': 无法推导出 'const std::basic_string<_Elem 的模板参数,_Traits,_Alloc>&'来自'const GUID

我知道我应该在这种情况下重载 operator <，但问题是我无权访问我想要使用的结构的代码 (GUID VC++ 中的结构).

I understand that I should overload operator < for that case, but the thing is I don't have access to the code of the structure I want to use (GUID structure in VC++).

这是代码片段:

//.h

#include <map>
using namespace std;

map<GUID,GUID> mapGUID;


//.cpp

GUID tempObj1, tempObj2;              
mapGUID.insert( pair<GUID,GUID>(tempObj1, tempObj2) );   

如何解决这个问题?

推荐答案

您可以将比较运算符定义为独立函数:

You can define the comparison operator as a freestanding function:

bool operator<(const GUID & Left, const GUID & Right)
{
    // comparison logic goes here
}

或者，因为通常 a <运算符对 GUID 没有多大意义，您可以改为提供自定义比较函子作为 std::map 模板的第三个参数:

Or, since in general a < operator does not make much sense for GUIDs, you could instead provide a custom comparison functor as the third argument of the std::map template:

struct GUIDComparer
{
    bool operator()(const GUID & Left, const GUID & Right) const
    {
        // comparison logic goes here
    }
};

// ...

std::map<GUID, GUID, GUIDComparer> mapGUID;

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