STL map详解-优快云博客

本文链接：https://blog.youkuaiyun.com/sinat_36629696/article/details/81610375

STL-map

map的构造

// 1. 默认构造
explicit map (const key_compare& comp = key_compare(),
              const allocator_type& alloc = allocator_type());
// 2. 迭代器构造
template <class InputIterator>
map (InputIterator first, InputIterator last,
     const key_compare& comp = key_compare(),
     const allocator_type& alloc = allocator_type());
// 3. 拷贝构造
map (const map& x);

map的迭代器

iterator begin();
const_iterator begin() const;

反向迭代器

reverse_iterator rbegin();
const_reverse_iterator rbegin() const;

C++11 cbegin() cend()

const_iterator cbegin() const noexcept;
const_iterator cend() const noexcept;

返回一个 const 迭代器, 不能用于修改元素

#include <iostream>
#include <map>

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

    mymap['b'] = 100;
    mymap['a'] = 200;
    mymap['c'] = 300;

    std::cout << "mymap contains:" << std::endl;
    for (auto it = mymap.cbegin(); it != mymap.cend(); ++it)
        std::cout << " [" << (*it).first << ':' << (*it).second << ']' << std::endl;
    std::cout << '\n';
    system("pause");
    return 0;
}

判空 empty 获取大小 size

operator[] : 根据 key 获得相应的 val

mapped_type& operator[] (const key_type& k);

如果 key 不存在, 返回空, 不会检查 key 的合法性

mapped_type& at (const key_type& k);
const mapped_type& at (const key_type& k) const;

作用和 operator[] 相似, 检查 key 的合法性, 如果 key 不存在会抛异常

举例:

// map 打印函数
template<class container>
void printContainer(container& s)
{
    typename container::const_iterator it = s.begin();
    // typename container::reverse_iterator it = s.rbegin();
    // while(it != s.end())
    while(it != s.end())
    {
        cout << it->first << " => " << it->second << endl;
        ++it;
    }
    cout << endl;
}


void TestMap01()
{
    // map 的构造
    // 1. 默认构造
    map<int, char> first;
    first[0] = 'a';
    first[1] = 'b';
    first[2] = 'c';
    first[3] = 'd';

    // 2, 拷贝构造
    map<int, char> second(first);

    // 3. 迭代器构造
    map<int, char> third(first.begin(), first.end());

    // 打印 map
    printContainer(first);
    // print(second);

    if(!first.empty())
    {
        cout << first.size() << endl;
    }

    cout << first[0] << endl;
    // cout << first.at(5) << endl; // 会检查 key 的合法性, 抛异常
}

insert

pair<iterator,bool> insert (const value_type& val);

iterator insert (iterator position, const value_type& val);

template <class InputIterator>
void insert (InputIterator first, InputIterator last);

erase

void erase (iterator position);

size_type erase (const key_type& k);

void erase (iterator first, iterator last);

clear

void clear();

清空 map 中的元素

举例:

void TestMap02()
{
    // 插入
    map<int, char> mymap;
    mymap.insert(pair<int, char>(1, 'x'));
    mymap.insert(pair<int, char>(2, 'y'));
    mymap.insert(pair<int, char>(3, 'z'));
    printContainer(mymap);
    pair<map<int, char>::iterator, bool> ret;
    ret = mymap.insert(pair<int, char>(3, 'v'));
    if(ret.second == false)
    {
        cout << "3 已经存在, 对应的 val => " << ret.first->second << endl;
    }

    map<int, char>::iterator it = mymap.begin();
    mymap.insert(it, pair<int, char>(4, 'b'));
    mymap.insert(it, pair<int, char>(5, 'n'));
    printContainer(mymap);

    map<int, char> othermap;
    othermap.insert(mymap.begin(), mymap.find(4)); // 从mymap的第一个到 4 的前一个
    printContainer(othermap);

    // 删除
    mymap.erase(2); // 指定 key 删除
    printContainer(mymap);
    it = mymap.find(5);
    mymap.erase(it); // 根据 find 返回的迭代器删除
    printContainer(mymap);
    it = mymap.find(1);
    mymap.erase(it, mymap.end()); // 删除一个区间
    printContainer(mymap);
    cout << "mymap size: " << mymap.size() << endl;

    cout << "othermap size: " << othermap.size() << endl;
    othermap.clear();
    cout << "othermap size: " << othermap.size() << endl;

}

find

iterator find (const key_type& k);
const_iterator find (const key_type& k) const;

返回元素的迭代器

count

size_type count (const key_type& k) const;

判断 key 是否存在, 存在返回 1, 不存在返回 0

插入

  template <class T1,class T2>
  pair<T1,T2> make_pair (T1 x, T2 y)
  {
      return ( pair<T1,T2>(x,y) );
  }

void TestMap_WaterMargin()
{

    map <string, string> mymap;
    mymap.insert(pair<string, string>("宋江", "及时雨"));
    mymap.insert(pair<string, string>("吴用", "智多星"));
    mymap.insert(make_pair("李逵", "黑旋风"));
    mymap.insert(make_pair("武松", "行者"));
    mymap.insert(make_pair("鲁智深", "花和尚"));
    cout << "Map size: " << mymap.size() << endl;
    // 插入 key 存在, val 不同的元素
    mymap.insert(make_pair("李逵", "铁牛"));
    cout << "Map size: " << mymap.size() << endl;
    printContainer(mymap);

    // 通过 key 查找 val
    cout << "武松: " << mymap["武松"] << endl;

    // 修改 key 对应的 val
    cout << "李逵: " << mymap["李逵"] << endl;
    mymap["李逵"] = "铁牛";
    cout << "李逵: " << mymap["李逵"] << endl;

    // 通过 [] 访问 key 对应的 val 时, 如果 key 不存在, 会创建一个默认 val 的键值对
    cout << "武大郎: " << mymap["武大郎"] << endl;
    cout << "Map size: " << mymap.size() << endl;
    cout << "武大郎: " << mymap["武大郎"] << endl; // val 默认为空

    // 删除
    mymap.erase(mymap.find("武大郎"));
    cout << "Map size: " << mymap.size() << endl;

    // 清空
    mymap.clear();
    cout << "Map size: " << mymap.size() << endl;
}

multimap

与 map 唯一的区别就是 key 可以重复

void TestMultiMap()
{
    multimap <string, string> mymap;
    mymap.insert(pair<string, string>("宋江", "及时雨"));
    mymap.insert(pair<string, string>("吴用", "智多星"));
    mymap.insert(make_pair("李逵", "黑旋风"));
    mymap.insert(make_pair("武松", "行者"));
    mymap.insert(make_pair("鲁智深", "花和尚"));
    printContainer(mymap);

    cout << "Map size: " << mymap.size() << endl;
    // 插入 key 存在, val 不同的元素
    mymap.insert(make_pair("李逵", "铁牛"));
    cout << "Map size: " << mymap.size() << endl;
    printContainer(mymap);

    multimap <int, int> m;
    for(int i=0; i<10; i++)
    {
        m.insert(make_pair(i, i));
    }
    m.insert(make_pair(5, 11));
    m.insert(make_pair(5, 12));
    m.insert(make_pair(5, 13));
    m.insert(make_pair(5, 14));

    printContainer(m);
    cout << "key 为 5 的元素个数: " << m.count(5) << endl;

    multimap<int, int>::iterator it;
    it = m.lower_bound(5);
    cout << it->first << " -> " << it->second << endl;
    it = m.upper_bound(5);
    cout << it->first << " -> " << it->second << endl;

    cout << endl;

    typedef multimap<int, int>::iterator Iter;
    pair<Iter, Iter> ret = m.equal_range(5);
    cout << ret.first->first << " -> " << ret.first->second << endl;
    cout << ret.second->first << " -> " << ret.second->second << endl;
}