STL中map的使用

#include <iostream>
#include <map>

//Maps are typically implemented as binary search trees. 
using namespace std;
ostream&operator<<(ostream&o,const pair<int,double>&p)
{
	o<<"("<<p.first<<","<<p.second<<")";
	return o;	//返回的是字符'o'不是零0 
}
int main()
{
	typedef map<int,double,less<int> >mmid;
	mmid pairs;
	cout<<"1)"<<pairs.count(15)<<endl;
	pairs.insert(mmid::value_type(15,2.7));		//typedef pair<const Key, T> value_type; 
	pairs.insert(make_pair(15,99.3));			//显然没有插入成功 
	cout<<"2)"<<pairs.count(15)<<endl;
	pairs.insert(mmid::value_type(20,9.3));
	mmid::iterator i;
	cout<<"3)";
	for(i=pairs.begin();i!=pairs.end();i++)
		cout<<*i<<",";
	cout<<endl;
	cout<<"4)";
	int n=pairs[40];	//如果没有key为40的元素，就插入一个 值value默认为0 
	for(i=pairs.begin();i!=pairs.end();i++)
		cout<<*i<<",";
	cout<<endl;
	cout<<"5)";
	pairs[15]=6.28;		//把key为15的元素的值value改为6.28 
	for(i=pairs.begin();i!=pairs.end();i++)
		cout<<*i<<",";
	return 0;
		
}