# map

就是一個對應表的概念，一對一的形式，跨越型態的限制

# 標頭檔

#include<map>

# 構造器 && 初始化

默認構造器： empty container constructor
範圍構造器： range constructor
複製構造器： copy constructor

	#include <iostream>
	#include <map>
	struct classcomp {
	bool operator() (const char& lhs, const char& rhs) const
	{return lhs<rhs;}
	};

	int main (){
	map<char,int> first; // 默認構造器

	first['a']=10;
	first['b']=30;
	first['c']=50;
	first['d']=70;

	map<char,int> second (first.begin(),first.end()); // 範圍構造器
	map<char,int> third (second); // 複製構造器
	map<char,int,classcomp> fourth; // 有自訂比較函式的構造器
	}

# 下標操作

map 最常使用的方法就只是直接使用 mp [ A ] = B 的方式互相對應

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

	int main (){
	map<char,string> mymap;

	mymap['a']="an element";
	mymap['b']="another element";
	mymap['c']=mymap['b'];

	cout << "mymap['a'] is " << mymap['a'] << '\n';
	cout << "mymap['b'] is " << mymap['b'] << '\n';
	cout << "mymap['c'] is " << mymap['c'] << '\n';
	cout << "mymap['d'] is " << mymap['d'] << '\n';

	cout << "mymap now contains " << mymap.size() << " elements.\n";
	}

# `insert`

重載函數	形参
插入單個值	pair<iterator,bool> insert (const value_type& val);
有位置提示	iterator insert (const_iterator position, const value_type& val);
範圍	templatevoid insert (InputIterator first, InputIterator last);

	#include <iostream>
	#include <map>
	using namespace std;

	void print(map<char,int>tmp){
	for (auto it : tmp)
	cout << it.first << " => " << it.second << '\n';
	}

	int main (){
	map<char,int> mymap;

	// 單個值插入
	mymap.insert ( pair<char,int>('a',100) );
	mymap.insert ( pair<char,int>('z',200) );

	pair<map<char,int>::iterator,bool> ret;
	ret = mymap.insert ( pair<char,int>('z',500) );
	if (ret.second==false) {
	cout << "元素 'z' 已經存在了";
	cout << " 他的值為: " << ret.first->second << '\n';
	}

	// 有位置提示的插入
	map<char,int>::iterator it = mymap.begin();
	mymap.insert (it, pair<char,int>('b',300)); // 最有效率的插入
	mymap.insert (it, pair<char,int>('c',400)); // 比較沒有效率的插入

	// 範圍型插入
	map<char,int> anothermap;
	anothermap.insert(mymap.begin(),mymap.find('c'));

	// 顯示內容物
	cout << "mymap contains:\n";
	print(mymap);

	cout << "anothermap contains:\n";
	print(anothermap);
	}

輸出

元素 'z' 已經存在了，他的值為: 200
mymap contains:
a => 100
b => 300
c => 400
z => 200
anothermap contains:
a => 100
b => 300

# `erase`

map 刪除已存元素的方式，常見共有三種。

	#include <iostream>
	#include <map>
	using namespace std;

	int main ()
	{
	map<char,int> mymap;
	map<char,int>::iterator it;

	mymap['a']=10;
	mymap['b']=20;
	mymap['c']=30;
	mymap['d']=40;
	mymap['e']=50;
	mymap['f']=60;

	it=mymap.find('b');
	mymap.erase (it); // 用指標清除

	mymap.erase ('c'); // 用 key 值清除

	it=mymap.find ('e');
	mymap.erase ( it, mymap.end() ); // 範圍型清除

	// 展示
	print(mymap);

	return 0;
	}

輸出

a => 10
d => 40

# `find`

尋找 map 中某一個 key 值的位置，如果找到的位置為 mp.end() 代表尚未找到

	#include <iostream>
	#include <map>
	using namespace std;

	int main (){
	map<char,int> mymap;
	map<char,int>::iterator it;

	mymap['a']=50;
	mymap['b']=100;
	mymap['c']=150;
	mymap['d']=200;

	it = mymap.find('b');
	if (it != mymap.end())
	mymap.erase (it);

	cout << "elements in mymap:" << '\n';
	cout << "a => " << mymap.find('a')->second << '\n';
	cout << "c => " << mymap.find('c')->second << '\n';
	cout << "d => " << mymap.find('d')->second << '\n';

	return 0;
	}

輸出

elements in mymap:
a => 50
c => 150
d => 200

# `count`

判斷 map 中，key 值是否已出現

	#include <iostream>
	#include <map>
	using namespace std;

	int main (){
	map<char,int> mymap;
	char c;

	mymap ['a']=101;
	mymap ['c']=202;
	mymap ['f']=303;

	for (c='a'; c<='g'; c++){
	cout << c;
	if (mymap.count(c))
	cout << " is an element of mymap.\n";
	else
	cout << " is not an element of mymap.\n";
	}
	return 0;
	}

輸出

a is an element of mymap.
b is not an element of mymap.
c is an element of mymap.
d is not an element of mymap.
e is not an element of mymap.
f is an element of mymap.
g is not an element of mymap.

# `clear`

清除整個 map 的工具

	#include <iostream>
	#include <map>
	using namespace std;

	int main (){
	map<char,int> mymap;

	mymap['x']=100;
	mymap['y']=200;
	mymap['z']=300;

	cout << "mymap contains:\n";
	print(mymap);

	mymap.clear();
	mymap['a']=1101;
	mymap['b']=2202;

	cout << "mymap contains:\n";
	print(mymap);`
	}

輸出

mymap contains:
x => 100
y => 200
z => 300
mymap contains:
a => 1101
b => 2202

# `empty`

如果 map 為空， empty 返回 true ;

# `size`

返回 map 容器元素個數

# multimap

就是一個對應表的概念，一對多的形式，跨越型態的限制

# 標頭檔

#include<map>

# 使用

跟 map 的操作大部分相同，但不能使用 下標[] 功能，插入值僅能用 insert

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

	void print(multimap<int,string>tmp){
	for (auto it : tmp)
	cout << it.first << " => " << it.second << '\n';
	}

	int main(){
	multimap<int, string> mapStudent;

	mapStudent.insert(pair<int, string>(101, "林小明"));
	mapStudent.insert(pair<int, string>(101, "王大明"));/// 一對多
	mapStudent.insert(pair<int, string>(102, "張大同"));
	mapStudent.insert(pair<int, string>(102, "葉哈囉"));
	mapStudent.insert(pair<int, string>(103, "李小龍"));
	mapStudent.insert(pair<int, string>(103, "陳小山"));
	mapStudent.insert(pair<int, string>(103, "黃中間"));

	cout << "mapStudent.size() is " << mapStudent.size() << endl << endl;

	print(mapStudent);
	}

輸出

mapStudent.size() is 7

101 => 林小明
101 => 王大明
102 => 張大同
102 => 葉哈囉
103 => 李小龍
103 => 陳小山
103 => 黃中間

STL C++ 自主學習程式語言筆記

# map

# 標頭檔

# 構造器 && 初始化

# 下標操作

# insert

# erase

# find

# count

# clear

# empty

# size

# multimap

# 標頭檔

# 使用

第06課、set的使用

1010 . Prefix and Postfix

# `insert`

# `erase`

# `find`

# `count`

# `clear`

# `empty`

# `size`