不能将STL映射与struct一起用作键吗? [英] Is it impossible to use an STL map together with a struct as key?

问题描述

我有以下代码:

struct Node
{
  int a;
  int b;
};

Node node;
node.a = 2;
node.b = 3;

map<int, int> aa;
aa[1]=1; // OK.

map<Node, int> bb;
bb[node]=1; // Compile error.

当我尝试将结构Node的实例映射到int时，出现编译错误.为什么?

When I tried to map an instance of my struct Node to an int, I got a compile error. Why?

推荐答案

要使某事物可用作地图中的键，您必须能够使用operator<()对其进行比较.您需要在节点类中添加这样的运算符:

For a thing to be usable as a key in a map, you have to be able to compare it using operator<(). You need to add such an operator to your node class:

struct Node
{
 int a;
 int b;

 bool operator<( const Node & n ) const {
   return this->a < n.a;   // for example
 }
};

当然，真正的运算符做什么取决于比较实际上对您的结构意味着什么.

Of course, what the real operator does depends on what comparison actually means for your struct.

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