STL标准库-容器-map和multimap

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map与multimap为关联容器,结构如下

map底层实现依然是rb_tree 他的data可以改,但是key不能改,因此map仍然具有自动排序的功能

我们无法使用迭代器改变元素的key(const key),但是可以改变元素的data.

map的key必须独一无二,multimap的key可以重复

map的定义函数

  template <typename _Key, typename _Tp, typename _Compare = std::less<_Key>,
            typename _Alloc = std::allocator<std::pair<const _Key, _Tp> > >
    class map
    {
    public:
      typedef _Key                                          key_type;
      typedef _Tp                                           mapped_type;
      typedef std::pair<const _Key, _Tp>                    value_type;
      typedef _Compare                                      key_compare;
      typedef _Alloc                                        allocator_type;
      ...
}

参数1 class key 键值key

参数2 class T data

参数3 class compare 排序key的函数 默认为less() 升序

参数4 alloc 分配器

---

map的基本使用

一 定义

    //构造函数
    map<int, int> c;
    c[] = ;
    c[] = ;
    c[] = ;
    c[] = ;
    c[] = ;
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //operator =
    map<int, int> c1;
    c1 = c;
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;

---

二 迭代器操作 map的迭代器就是红黑树的迭代器

    //迭代器操作
    /*
    map<int, int> c;
    c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
    */
 
    //begin()
    map<int, int>::iterator iter;
    iter = c.begin();
    cout<< "begin(): "<<"["<< iter->first <<"] = " << iter->second <<endl;
 
    //end()
    iter = c.end();
    iter--;
    cout<<"end(): " <<"["<< iter->first <<"] = " << iter->second <<endl;
 
    //rbegin()反向头迭代器
    map<int, int>::reverse_iterator riter;
    riter = c.rbegin();
    cout << "rbegin(): "<<"["<< riter->first <<"] = " << riter->second <<endl;
 
    //rend()反向头迭代器
    riter = c.rend();
    riter--;
    cout << "rend(): "<<"["<< riter->first <<"] = " << riter->second <<endl;
 
    //cbegin() const 迭代器 正向 头迭代器
    map<int, int>::const_iterator citer;
    citer = c.cbegin();
    cout << "cbegin(): "<<"["<< citer->first <<"] = " << citer->second <<endl;
 
    //cend() const 迭代器 反向 尾迭代器
    citer = c.cend();
    citer--;
    cout<< "cend(): "<<"["<< citer->first <<"] = " << citer->second <<endl;

---

三 容量

    //容量
    /*
     map<int, int> c;
     c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
     */
    //是否为kong
    cout << "empty: " << c.empty() <<endl;
 
    //元素个数
    cout << "size: " << c.size() <<endl;
 
    //最大容量
    cout << "max_size: " << c.max_size() <<endl;

---

四 基本操作

//基本操作
    /*
     map<int, int> c;
     c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
     */
 
    //operator[] 这个和其他容器的operator有些不同,如果[index] 的index(key) 在map中存在则直接返回该key对应的data ,如果不存在则想该位置插入默认值
    cout << "operator[]: " << c[] << endl;
    cout << "operator[]: " << c[] << endl; //这时你会发现 map自动插入一个c[10]
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //at() 取data
    cout<< "at(): " << c.at() << endl;
 
    //插入insert() map 不允许key重复 插入重复key 不会报错但插入不成功
    c.insert(pair<int, int>(, ));
    cout <<"insetr(): ";
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    map<int, int> c_insert;
    map<int, int>::iterator insert_iter = c_insert.begin();
    c_insert.insert(insert_iter,pair<int, int>(, ));
    cout <<"insetr(): ";
    for(auto i : c_insert)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //删除
    map<int,int>::iterator erase_iter = c.begin();
    c.erase(erase_iter);
    cout <<"erase(): ";
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
    //指定下表删除
    c.erase();
    cout <<"erase(): ";
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //指定元素删除
    erase_iter = c.find();
    if(erase_iter != c.end())
    {
        cout<<"found index: "<< erase_iter->first <<endl;
        c.erase(erase_iter);
    }
    else{
        cout<< "Not found" <<endl;
    }
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //交换swap
    map<int, int> c_swap1;
    c_swap1.insert({pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,)});
    map<int, int> c_swap2;
    cout<<"swap() before: "<<endl;
    cout<<"c_swap1: ";
    for(auto i : c_swap1)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    cout<<"c_swap2: ";
    for(auto i : c_swap2)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    cout<<"swap() after: ";
    c_swap2.swap(c_swap1);
    cout<<"c_swap1: ";
    for(auto i : c_swap1)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    cout<<"c_swap2: ";
    for(auto i : c_swap2)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //清除clear
    c_insert.clear();
    cout <<"clear(): ";
    for(auto i : c_insert)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //elements() 插入 如果存在什么也不做 如果不存在插入
    map<int, int>::iterator element_iter = c_swap2.begin();
 
    auto xxx = c_swap2.emplace(pair<int, int>(,));
    if(xxx.second)
    {
        cout << "不存在" <<endl;
    }
    else
    {
        cout<< "存在" <<endl;
    }
    cout <<"elements(): ";
    for(auto i : c_swap2)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //emplace_hint() 插入
    element_iter = c.emplace_hint(element_iter, pair<int, int>(,));
    cout <<"emplace_hint(): ";
    if(element_iter != c_swap2.end())
    {
        cout<< "存在" <<endl;
    }
    else{
        cout << "不存在" <<endl;
    }

---

五 操作函数

    //函数
    /*
     map<int, int> c;
     c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
     */
    //key_comp 返回key排序的函数 返回仿函数
    cout<<"key_comp(): " << c.key_comp()(,) <<endl; //会返回1  因为1<2
    cout<<"key_comp(): " << c.key_comp()(,) <<endl; //会返回0  因为2>1
    cout<<"key_comp(): " << c.key_comp()(,) <<endl; //会返回0  因为1=1
 
    //value_comp 返回取value和key数据包中的 取key函数 返回仿函数
    pair<int,int> value_comp_pair = *c.begin();
    iter = c.begin();
    cout << c.value_comp()(*iter++,value_comp_pair) << endl;

---

六 算法

//算法
    /*
     map<int, int> c;
     c.insert({pair<int, int>(1,10),pair<int, int>(2,20),pair<int, int>(3,30),pair<int, int>(4,40),pair<int, int>(5,50),pair<int, int>(6,60)});
     */
    //find()  指定key 返回对应pair
    cout <<"find(1): " << c.find()->second << endl;;
 
    //count()   key出现的次数
    cout <<"count(1): " << c.count()<< endl;;
 
    c.erase();
 
    //lower_bound 返回键值>=给定元素的第一个位置
    auto lower_boundObj = c.lower_bound();
    if(lower_boundObj->first)
        cout<<lower_boundObj->first<<endl;
    else
        cout<< "Not found lower_boundObj" << endl;
 
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //upper_bound 返回键值>给定元素的第一个位置
    auto upper_boundObj = c.upper_bound();
    if(upper_boundObj->first)
        cout<<upper_boundObj->first<<endl;
    else
        cout<< "Not found upper_bound" << endl;
 
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
 
    //equal_range()返回该元素所在区间(闭区间),返回值是一个pair<iterator, iterator>类型,first代表所在区间的起点迭代器,second表示所在区间的终点迭代器
 
    auto equal_rangeObj = c.equal_range();
    if(equal_rangeObj.first->first)
    {
        cout<<equal_rangeObj.first->first<<endl;
    }
    else
        cout<< "NOT equal_rangeObj.first" << endl;
 
    if(equal_rangeObj.second->second)
    {
        cout<<equal_rangeObj.second->first<<endl;
    }
    else
        cout<< "NOT second" << endl;

---

七 自定义比较函数 map 默认为升序 改为降序

class my_compare_
{
public:
    bool operator()(int a, int b)
    {
        return a > b;
    }
};
 
int main(int argc, char *argv[])
{
    map<int, int, my_compare_> c;
    c.insert({pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,),pair<int, int>(,)});
    for(auto i : c)
    {
        cout<<"["<< i.first <<"] = " << i.second <<"  ";
    }
    cout << endl;
    return ;
}