STL学习(六)--map/multimap用法详解

两者的内部结构都是用的是平衡二叉树，区别在于multimap允许重复元素而map不允许。

map和multimap**根据元素的key**自动对元素进行排序，要修改元素的key必须先删除拥有该key的元素，然后插入拥有新的key/value的元素

常用函数:

(1)构造函数和析构函数

(2)大小判空函数

(3)增加删除函数(注意insert一般用pair)mymap.insert(it,pair

#include <iostream>
#include <map>

using namespace std;

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

mymap.insert(pair<char, int>('a', 10));
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 << "element 'z' already existed";
cout << "with a value of " << ret.first->second << '\n';
}

map<char, int>::iterator it = mymap.begin();
mymap.insert(it, pair<char, int>('b', 300));
mymap.insert(it, pair<char, int>('c', 400));

map<char, int> anothermap;
anothermap.insert(mymap.begin(), mymap.find('c'));

cout << "mymap contains :\n";
for (it = mymap.begin(); it != mymap.end(); it++)
{
cout << it->first << "=>" << it->second << '\n';
}

cout << "anothermap contains :\n";
for (it = anothermap.begin(); it != anothermap.end(); it++)
{
cout << it->first << "=>" << it->second << '\n';
}
return 0;
}

关于删除函数的应用

#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.insert(pair<char, int>('f', 60));

cout << "initial mymap contains :\n";
for (it = mymap.begin(); it != mymap.end(); it++)
{
cout << it->first << "=>" << it->second << '\n';
}

it = mymap.find('b');
mymap.erase(it);

mymap.erase('c');

it = mymap.find('e');
mymap.erase(it, mymap.end());
//删除的是it到end()之间的元素
cout << "now mymap contains :\n";
for (it = mymap.begin(); it != mymap.end(); it++)
{
cout << it->first << "=>" << it->second << '\n';
}

return 0;
}

如果想往map/multimap中修改一个映射的值，应先插入一个新映射，再把与修改的映射删除

4.遍历函数

5.操作函数

const_iterator lower_bound(const Key& key);//返回键值小于等于key的迭代器指针

6.特殊函数

reference operator[](const Key& k);仅在单映射map类中，可以以数组的形式给映射添加键值对，并可返回值的引用

实例:

map<char, int> mymap;

mymap['a'] = 10;
mymap['b'] = 20;
mymap['c'] = 30;
mymap['d'] = 40;