1.map
- map容器中所有的元素都是键值对，即pair
- pair中的第一个元素为键值，第二个元素为value
- 所有的元素会根据元素的键值自动排序
- 不允许容器中有重复的key值，multimap容器允许有重复的key值
- 属于关联式容器，底层结构为二叉树
1.map容器的构造与赋值
构造：
map<T1, T2> mp; //map默认构造函数:
map(const map &mp); //拷贝构造函数
赋值操作：
map& operator=(const map &mp); //重载等号操作符
例子
#include <iostream>
#include <map>
using namespace std;
void printMap(map<int, int>& m)
{
for (auto item : m)
{
cout << "item.first = " << item.first << endl;
cout << "item.second = " << item.second << endl;
}
#if 0
for (auto it = m.begin();it != m.end(); ++it)
{
cout << "it->first = " << it->first << endl;
cout << "it->second = " << it->second << endl;
}
#endif
}
int main()
{
map<int, int> m;
m.insert(pair<int, int>(1, 2));
m.insert(pair<int, int>(3, 4));
m.insert(pair<int, int>(5, 6));
printMap(m);
map<int, int>m2(m);
cout << "++++++++++cout m2+++++++++" << endl;
printMap(m2);
cout << "++++++++++cout m3+++++++++" << endl;
map<int, int>m3;
m3 = m2;
printMap(m3);
}
结果：
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
++++++++++cout m2+++++++++
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
++++++++++cout m3+++++++++
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
2.map大小与交换
size():返回容器中元素的个数
empty():判断容器是否为空
swap(st):交换两个集合容器,空间不一样也可使用
例子：
#include <iostream>
#include <map>
using namespace std;
void printMap(map<int, int>& m)
{
for (auto item : m)
{
cout << "item.first = " << item.first << endl;
cout << "item.second = " << item.second << endl;
}
#if 0
for (auto it = m.begin();it != m.end(); ++it)
{
cout << "it->first = " << it->first << endl;
cout << "it->second = " << it->second << endl;
}
#endif
}
int main()
{
map<int, int> m;
m.insert(pair<int, int>(1, 2));
m.insert(pair<int, int>(3, 4));
m.insert(pair<int, int>(5, 6));
cout << "m.size=" << m.size() << endl;
if (m.empty())
{
cout << "m is empty" << endl;
}
else
{
cout << "m is not empty" << endl;
}
printMap(m);
map<int, int>m2;
m2.insert(pair<int, int>(7, 8));
m.swap(m2);
cout << "++++++++++cout m2+++++++++" << endl;
printMap(m2);
cout << "++++++++++cout m1+++++++++" << endl;
printMap(m);
}
结果：
m.size=3
m is not empty
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
++++++++++cout m2+++++++++
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
++++++++++cout m1+++++++++
item.first = 7
item.second = 8
3.map容器的插入与删除
insert(elem); //在容器中插入元素。
clear();//清空所有元素
erase(pos);//删除pos迭代器所指元素，返回下一个元素的迭代器
erase(beg, end); //删除区间[beg,end)的所有元素 ，返回下一个元素的迭代器。
erase(key); //删除容器中值为key的元素。
代码示例：
#include <iostream>
#include <map>
using namespace std;
void printMap(map<int, int>& m)
{
for (auto item : m)
{
cout << "item.first = " << item.first << endl;
cout << "item.second = " << item.second << endl;
}
#if 0
for (auto it = m.begin();it != m.end(); ++it)
{
cout << "it->first = " << it->first << endl;
cout << "it->second = " << it->second << endl;
}
#endif
}
int main()
{
map<int, int> m;
//1.first insert method1
m.insert(pair<int, int>(1, 2));
//2.sencond
m.insert(make_pair(3, 4));
//3.
m.insert(map<int,int>::value_type(5, 6));
cout<<"-----------------------------------m----------------------------------------"<<endl;
printMap(m);
//erase
cout<<"------------------------erase begin and 3------------------------------------"<<endl;
m.erase(m.begin());
m.erase(3);
printMap(m);
cout << "--------------------erase all----------------------------------------------"<<endl;
m.erase(m.begin(),m.end());
printMap(m);
}
编译：
g++ map_insert.cpp -std=c++11 -o map_insert
结果：
-----------------------------------m----------------------------------------
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
------------------------erase begin and 3------------------------------------
item.first = 5
item.second = 6
--------------------erase all----------------------------------------------
4.map容器的查找与统计
find(key)//m.find(key),查找key元素是否存在，返回改元素的迭代器，若不存在，则返回set.end()
count(key)//统计key的元素个数,对于map只有0和1
示例：
#include <iostream>
#include <map>
using namespace std;
void printMap(map<int, int>& m)
{
for (auto item : m)
{
cout << "item.first = " << item.first << endl;
cout << "item.second = " << item.second << endl;
}
#if 0
for (auto it = m.begin();it != m.end(); ++it)
{
cout << "it->first = " << it->first << endl;
cout << "it->second = " << it->second << endl;
}
#endif
}
int main()
{
map<int, int> m;
//1.first insert method1
m.insert(pair<int, int>(1, 2));
//2.sencond
m.insert(make_pair(3, 4));
//3.
m.insert(map<int,int>::value_type(5, 6));
cout <<"-----------------------------------m----------------------------------------" <<endl;
printMap(m);
//查找
cout<<"------------------------find 3------------------------------------"<<endl;
auto it=m.find(3);
if(it != m.end())
{
cout<<"key 3 value is=" << it->second << endl;
}
cout << "--------------------count 3----------------------------------------------"<<endl;
int num = m.count(3);
cout << "count 3 is=" << num << endl;
}
结果：
-----------------------------------m----------------------------------------
item.first = 1
item.second = 2
item.first = 3
item.second = 4
item.first = 5
item.second = 6
------------------------find 3------------------------------------
key 3 value is=4
--------------------count 3----------------------------------------------
count 3 is=1
5.map容器的排序
map容器默认为按照key值小到大进行排序，但是我们可以利用仿函数进行从大到小进行排序
示例：
#include <iostream>
#include <map>
using namespace std;
class BigToSmall
{
public:
bool operator()(int a,int b)
{
return a > b;
}
};
void printMap(map<int, int,BigToSmall>& m)
{
cout << "-------------------sort---------------------"<<endl;
for (auto item : m)
{
cout << "item.first = " << item.first << endl;
cout << "item.second = " << item.second << endl;
}
#if 0
cout << "---------------------sort----------------------"<<endl;
for (map<int,int,BigToSmall>:: iterator it= m.begin();it != m.end(); ++it)
{
cout << "it->first = " << it->first << endl;
cout << "it->second = " << it->second << endl;
}
#endif
}
int main()
{
map<int, int,BigToSmall> m;
//1.first insert method1
m.insert(pair<int, int>(1, 2));
m.insert(pair<int,int>(7,8));
//2.sencond
m.insert(make_pair(3, 4));
//3.
m.insert(map<int,int>::value_type(5, 6));
printMap(m);
}
结果：
------------------sort---------------------
item.first = 7
item.second = 8
item.first = 5
item.second = 6
item.first = 3
item.second = 4
item.first = 1
item.second = 2