map容器里面所有的元素都是pair对组。对组中第一个元素叫key(键值)，第二个元素叫value(实值)。和set容器一样，map容器也属于关联式容器，底层用二叉树实现，且所有的元素都会在插入时按键值自动排序。map和multimap的主要区别在于是否允许有重复的键值，map容器不允许有重复的键值，而multimap允许有重复的键值。
构造和赋值
函数原型
map<T1,T2>mp; //map默认构造函数 map<T1,T2>(const map &mp); //拷贝构造函数 map& operator=(const map &mp); //重载赋值操作符
void printMap(const map<int, int> &m)
{
for (map<int, int>::const_iterator it = m.begin(); it != m.end(); it++)
{
cout << "key = " << it->first << " value = " << it->second << endl;
}
}
void test01()
{
//创建map容器
map<int, int > m1;//第一个int代表key 第二个int代表value
m1.insert(pair<int, int>(1, 10));
m1.insert(pair<int, int>(2, 20));
m1.insert(pair<int, int>(4, 40));
m1.insert(pair<int, int>(5, 50));
m1.insert(pair<int, int>(3, 30));
m1.insert(pair<int, int>(6, 60));
printMap(m1); /*key = 1 value = 10
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40
key = 5 value = 50
key = 6 value = 60*/
//拷贝构造
map<int, int> m2(m1);
//赋值
map<int, int> m3;
m3 = m2;
}
map容器中所有的元素都是对组，对组中第一个元素是.first表示key值，第二个元素是.second表示value。
大小和交换
函数原型
size(); //返回容器大小 empty(); //判断容器是否为空 swap(sw); //交换两个集合容器
void printMap(const map<int, int> &m)
{
for (map<int, int>::const_iterator it = m.begin(); it != m.end(); it++)
{
cout << "key = " << it->first << " value = " << it->second << endl;
}
}
void test01()
{
map<int, int > m1;
m1.insert(pair<int, int>(1, 10));
m1.insert(pair<int, int>(2, 20));
m1.insert(pair<int, int>(4, 40));
m1.insert(pair<int, int>(5, 50));
m1.insert(pair<int, int>(3, 30));
m1.insert(pair<int, int>(6, 60));
if(m1.empty())
{
cout << "m1为空！" << endl;
}
else
{
cout << "m1不为空！" <<"大小为："<<m1.size()<< endl;
}
map<int, int> m2;
m2.insert(pair<int, int>(6, 60));
m2.insert(pair<int, int>(7, 70));
m2.insert(pair<int, int>(10, 100));
m2.insert(pair<int, int>(8, 80));
m2.insert(pair<int, int>(9, 90));
cout << "交换前：" << endl;
cout << "m1:" << endl;
printMap(m1); /*key = 1 value = 10
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40
key = 5 value = 50
key = 6 value = 60*/
cout << "m2:" << endl;
printMap(m2); /*key = 6 value = 60
key = 7 value = 70
key = 8 value = 80
key = 9 value = 90
key = 10 value = 100*/
//交换
m1.swap(m2);
cout << "交换后：" << endl;
cout << "m1:" << endl;
printMap(m1); /*key = 6 value = 60
key = 7 value = 70
key = 8 value = 80
key = 9 value = 90
key = 10 value = 100*/
cout << "m2:" << endl;
printMap(m2); /*key = 1 value = 10
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40
key = 5 value = 50
key = 6 value = 60*/
}
插入和删除
函数原型
insert(elem); //在容器中插入元素 clear(); //清空所有元素 erase(pos); //删除pos迭代器所指的元素，返回下一个元素的迭代器 erase(begin,end) //删除[begin,end)区间所有的元素，返回下一个元素的迭代器 erase(key); //删除容器中值为key的元素
void printMap(const map<int, int> &m)
{
for (map<int, int>::const_iterator it = m.begin(); it != m.end(); it++)
{
cout << "key = " << it->first << " value = " << it->second << endl;
}
}
void test01()
{
map<int, int > m1;
m1.insert(pair<int, int>(1, 10)); //插入
m1.insert(make_pair(2, 20));
m1.insert(map<int, int>::value_type(3, 30));
m1[4] = 40; //key = 4 value = 40
printMap(m1); /*key = 1 value = 10
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40*/
cout << "++++++++++++++++++++++++++++++++++++++" << endl;
//删除
m1.erase(m1.begin());
printMap(m1); /*
key = 2 value = 20
key = 3 value = 30
key = 4 value = 40*/
cout << "++++++++++++++++++++++++++++++++++++++" << endl;
m1.erase(3); //删除key为3的元素
printMap(m1); /*key = 2 value = 20
key = 4 value = 40*/
cout << "++++++++++++++++++++++++++++++++++++++" << endl;
m1.clear(); //清空
cout << "容器大小为：" << m1.size() << endl;
}
erase有一个重载版本，erase(key)，要注意只能按key值删除，不能按value值删除。
查找和统计
函数原型
find(key); //查找key是否存在，若存在，返回该元素的迭代器；若不存在，返回end迭代器 count(key); //统计key的个数
void test01()
{
map<int, int > m1;
m1.insert(pair<int,int>(1,10));
m1.insert(pair<int,int>(2,20));
m1.insert(pair<int,int>(3,30));
m1.insert(pair<int,int>(4,40));
map<int, int>::iterator pos = m1.find(3); //查找key值为3的元素。
if (pos != m1.end())
{
cout << "找到元素key = " << (*pos).first << " value = " <<(*pos).second << endl;
}
else
{
cout << "未找到元素！" << endl;
}
int num = m1.count(2); //查找key值为2的元素
cout << " num = " << num << endl; //1 对于map容器而言，查找结果只能为1或0
}
对于map容器而言，查找到的结果只能是1或0；对于multimap而言，查找结果可以是其他数字。
map容器排序
map容器默认升序排列，但是也可以通过仿函数来修改默认排序规则为降序。
class Compare
{
public:
bool operator()(int val1, int val2) const
{
//降序
return val1 > val2;
}
};
void printMap(const map<int, int, Compare> &m)
{
for (map<int, int>::const_iterator it = m.begin(); it != m.end(); it++)
{
cout << "key = " << it->first << " value = " << it->second << endl;
}
}
void test01()
{
map<int, int,Compare > m1;
m1.insert(pair<int,int>(1,10));
m1.insert(pair<int,int>(2,20));
m1.insert(pair<int,int>(3,30));
m1.insert(pair<int,int>(4,40));
printMap(m1); /*key = 4 value = 40
key = 3 value = 30
key = 2 value = 20
key = 1 value = 10*/
}
