unordered_map

转载自： 

https://blog.csdn.net/hk2291976/article/details/51037095#332-insert

https://www.cnblogs.com/acbingo/p/4556427.html

1、基本操作：

#include<iostream>
#include<map>
#include<vector>
#include<unordered_map>
#include<string>
using namespace std;

void display(unordered_map<string, double> myrecipe, string str) {
	cout << str << endl;
	for (auto& x : myrecipe)
		cout << x.first << ":" << x.second << endl;
	cout << endl;
}
int main() {
	unordered_map<string, double> myrecipe, mypantry = { {"milk",2.0},{"flour",1.5} };
	pair<string, double> myshopping = { "baking powder",0.3 };
	/****************************插入********************************/
	//myrecipe.insert(pair<string,double("baking powder",0.3)>)
	myrecipe.insert(myshopping);//复制插入
	myrecipe.insert(make_pair<string, double>("eggs", 6.0));//移动插入
	myrecipe.insert(mypantry.begin(), mypantry.end());//范围插入
	myrecipe.insert({ {"suga",0.8},{"salt",0.1} });//初始化数组形势插入
	myrecipe["coffe"] = 1.0;//数组形式的插入

	display(myrecipe, "myrecipe contains:");
	/****************************查找********************************/
	unordered_map<string, double>::const_iterator got = myrecipe.find("coffe");
	if (got == myrecipe.end())
		cout << "not found" << endl;
	else
		cout << "Found " << got->first << " is " << got->second << endl;
	/****************************查找********************************/
	myrecipe.at("coffe") = 9.0;
	myrecipe["milk"] = 3.0;
	display(myrecipe, "After moddifing:");
	/****************************擦除********************************/
	myrecipe.erase(myrecipe.begin());
	myrecipe.erase("milk");
	display(myrecipe, "After erasing:");
	/****************************交换********************************/
	myrecipe.swap(mypantry);
	display(myrecipe, "After swapping:");
	/****************************清空********************************/
	myrecipe.clear();
	display(myrecipe, "After clearing:");
	while (1);
}

myrecipe contains:
baking powder:0.3
eggs:6
flour:1.5
milk:2
suga:0.8
salt:0.1
coffe:1

Found coffe is 1
After moddifing:
baking powder:0.3
eggs:6
flour:1.5
milk:3
suga:0.8
salt:0.1
coffe:9

After erasing:
eggs:6
flour:1.5
suga:0.8
salt:0.1
coffe:9

After swapping:
milk:2
flour:1.5

After clearing:

2、 make_pair

#include<iostream>
#include<algorithm>
#include<map>
#include<vector>
#include<unordered_map>
#include<string>
using namespace std;

bool cmp(const pair<int, string> a, const pair<int, string> b) {
	return a.first > b.first;//通过运算符重载，利用sort函数实现非升序排序
}
int main() {
	vector<pair<int, string>> vec;
	vec.push_back(make_pair<int, string>(5,"_bingo"));
	vec.push_back(make_pair<int, string>(4, "bin"));
	vec.push_back(make_pair<int, string>(6, "abc_bingo"));
	vec.push_back(make_pair<int, string>(6, "ABC_bingo"));
	vec[3].first++;
	cout << "Before sort:" << endl;
	for (auto element : vec)
		cout << element.first << ":" << element.second << endl;
	cout << endl;
	sort(vec.begin(), vec.end(),cmp);//sort默认是非降序排序，写入cmp函数，可以自定义排序方式
	for (auto element : vec)
		cout << element.first << ":" << element.second << endl;
	while (1);
}

Before sort:
5:_bingo
4:bin
6:abc_bingo
7:ABC_bingo

7:ABC_bingo
6:abc_bingo
5:_bingo
4:bin

 3、更多操作详见参考连接

 

更多hash函数相关知识：http://www.nowamagic.net/academy/detail/3008108