set的交换，赋值以及初始化

#include<iostream>
#include<set>
using namespace std;
struct dian{
	int x,y;
	/*bool operator<(const dian &a) const
	{
		return x<a.x;
	}*/
};
/* 自定义排序函数一定要用const*/
bool operator<(const dian &a,const dian &b)
{
	return a.x<b.x;
}
void swap(set<dian> &s1,set<dian> &s2)
{
	set<dian> s;
	s=s1;
	s1=s2;
	s2=s;
}
int main()
{
	set<dian> s1,s2;
	dian a;
	a.x=6;
	a.y=7;
	dian b;
	b.x=7;
	b.y=9;
	s1.insert(a);
	s1.insert(b);
//	s1.swap(s2);
//	swap(s2,s1); 
	s2=s1;
	set<dian> s(s2);
	for(auto i:s)
	{
		cout<<i.x<<" "<<i.y<<endl;
	}
}