map的基本操作和使用

#include<iostream>#include <map>#include <string>using namespace std;template <class Key,          class T,          class Compare = less<Key>,          class Alloc = allocator<pair<const, Key, T>>          > class map;*  map 是一种关联容器, 将键值和映射值组合成元素并且按照特定顺序进行排列, 通常键值用来排序和唯一标识元素, 映射值用来存储和键值相关的内容;*  键值类型和映射值类型不要求一样, 但是通常声明为typedef pair<const key, T> value_type;*  在按照键进行排序的过程中, 是按照内部比较对象指定的严格弱排序标准进行排序;*  map容器对于单个元素的访问通常比unordered_map容器慢, 但是允许按照迭代器进行迭代;* 对于map的构造函数一共有五种类型;* 1.empty containers constructors(默认构造函数): 用于构造一个空的map对象;    * 2.range constructors(): 范围构造函数用于将一个范围里面的元素[first, last], 每个元素    对应 容器里面的范围;    * 3.copy constructors(): 通过将原始元素进行拷贝来进行构造, 同时也会拷贝分配器;    * 4.move constructors(): 移动构造函数, 用于构建一个可以获得X的容器, 如果分配器的类型    不同于X, 元素会被移动, 否则, 不会进行任何的构造操作;* 5.initializer list constructor:    实际上是原来是元素的一个拷贝;    * 在map容器内部保持一个内部复制原则, 用来分配, 存储, 销毁等操作, 如果没有参数传递给构造函数, 那么使用默认的分配器, 但是存在以下几种情况是例外的:    * 1.对于复制构造函数在构建一个容器时, 不断调用, 并使用分配器;    * 2.对与移动构造函数也是例外;    * 所有的元素都是通过复制, 移动或者通过调用allocator_traits进行构造的;    bool fncomp(char lns, char rns){    return lns < rns;}struct clascomp{    bool operator()(const char& lns, const char& rns)const    {        return lns < rns;    }};int main(){    //constructors 的几种构建方式:    map<char, int> first;    first['a'] = 10;    first['b'] = 20;    first['c'] = 30;    first['d'] = 40;    map<char, int> second(first.begin(), first.end());    map<char, int> third(second);    map<char, int, clascomp> fourth;    bool(*fn_pt)(char, char) = fncomp;    map<char, int, bool(*)(char, char)> fifth(fn_pt);    //.at()用于返回对键k标识元素的映射值的引用,如果K在容器map里面不存在任何映射值,使    //用out_of_range抛出异常;相关函数的声明包括:mapped_type& at(const key_type& k);    //const mapped_type& at(const key_type& k)const;    map<string, int> mymap =    {        {"alpah", 0},        {"beta", 0},        {"gamma", 0}    };    mymap.at("alpah") = 10;    mymap.at("beta") = 20;    mymap.at("gamma") = 30;    cout << "mymap contains: ";    for (auto X : mymap)        cout << "(" << X.first << "," << X.second << ")" << " ";    cout << endl;    //.begin(),.end()用于访问里面元素的迭代器    cout << "mymap contains: ";    for (map<string, int>::iterator It = mymap.begin(); It != mymap.end(); ++It)        cout << "(" << It->first + "lixun" << " => " << It->second + 10 << ")" << " ";    cout << endl;    //.cbegin().cend() 表示不允许进行修改成员的值    cout << "mymap contains const: ";    for (auto It = mymap.cbegin(); It != mymap.cend(); ++It)        cout << "(" << It->first  << " => " << It->second << ")" << " ";    cout << endl;    //.rbegin()以及.rend()是用来进行反向遍历的迭代器;    cout << "mymap contains reverse: ";    for (auto It = mymap.rbegin(); It != mymap.rend(); ++It)        cout << "(" << It->first + "lixun" << " => " << It->second + 10 << ")" << " ";    cout << endl;    //.rcbegin()以及.rcend()是用来进行反向遍历的迭代器;    cout << "mymap contains reverse: ";    for (auto It = mymap.crbegin(); It != mymap.crend(); ++It)        cout << "(" << It->first << " => " << It->second << ")" << " ";    cout << endl;    //.clear()用于清空里面的元素,函数声明是:void clear() noexcept;    //.cout()在map里面查找一个和K相等的值,并且返回相等值的数量;    map<char, int> mymap1;    mymap1['a'] = 10;    mymap1['b'] = 9;    mymap1['c'] = 8;    char c;    for ( c = 'a'; c < 'g'; ++c)    {        cout << c << " ";        if (mymap1.count(c) > 0)            cout << "is an elememt of mymap1;" << endl;        else            cout << "is not an element of mymap1;" << endl;    }    //.emplace():template<class... Args) pair<iteraotr,bool> emplace(Arg&&...args);    //如果插入的值是不唯一的,那么就插入一个新的元素,参数的类型和pair的类型是一致的;    //如果插入成功,那么size就会增长,map里面的元素是按照对象指定的标准进行排序    //如果元素成功插入,那么就会返回一对迭代器插入元素后的新的位置;    //如果插入失败,那么就返回在map里面找到的和新插入元素相等的值的位置;    map<char, int> mymap2;    mymap2.emplace('x', 1);    mymap2.emplace('y', 2);    mymap2.emplace('z', 3);    mymap2.emplace('k', 4);    cout << "mymap2 contains: ";    for (auto &X : mymap2)        cout << "(" << X.first << ":" << X.second << ")" << " ";    cout << endl;    //.emplace_hint():再进行元素插入时可以指定一个位置进行元素的插入,对于元素插入的要求和    //.emplace()是一样的;    {        auto It = mymap2.end();        It = mymap2.emplace_hint(It, 'b', 11);        mymap2.emplace_hint(It, 'c', 12);        It = mymap2.begin();        mymap2.emplace_hint(It, '3', 19);        cout << "mymap2.emplace_hint contains: ";        for (auto X : mymap2)            cout << "(" << X.first << ":" << X.second << ")" << " ";        cout << endl;    }    //.empty()用于判断是否为空操作:bool empty()const noexcept;    //.equal_range() pair<const_iterator,const_iterator> equal_range(const key_type& k)const;    //pair<iterator,iterator> equal_range(const key_type& k);这些函数的作用是用来返回等价于    //元素K的范围的一个边界;因为map的特性,所以返回的元素只有一个,范围也只有一个;如果没有匹配    //到元素,那么就返回两个都指向第一个元素的迭代器,并且返回长度是0;    {        auto ret = mymap2.equal_range('b');        cout << "lower bound points to: ";        cout << ret.first->first << "=>" << ret.first->second << " ";        cout << endl;        cout << "upper bound points to: ";        cout << ret.second->first << "=>" << ret.second->second << " ";        cout << endl;    }    //.erase(): iterator erase(const_iterator position);    //size_type erase(const key_type& k);    //iterator erase(const_iterator first,const_iterator last);    //用于删除单个或者是某个范围里面的元素;    {        cout << "mymap2.erase() contains: ";        auto It = mymap2.find('b');        mymap2.erase(It);        mymap2.erase('x');        It = mymap2.find('k');        mymap2.erase(It,mymap2.end());        for(auto It=mymap2.begin();It!=mymap2.end();++It)            cout << It->first << "=>" << It->second << " ";        cout << endl;    }    //.find()用于查找某一个元素的位置,一共有两个版本:iterator find(const key_type& k);    //const_iterator find(const key_type& k)const;    //查找某一个元素的值,如果找不到,就返回最后一个元素的位置;    {        mymap2['s']=12;        mymap2['v']=11;        mymap2['l']=10;        mymap2['j']=9;        mymap2['t']=0;        auto It = mymap2.find('j');        if(It!=mymap2.end())            mymap2.erase(It);        cout << "mymap2.erase() contains: ";        cout << "s=>" << mymap2.find('s')->second << " ";        cout << "l=>" << mymap2.find('l')->second << " ";        cout << "j=>" << mymap2.find('j')->second << " ";        cout << "t=>" << mymap2.find('t')->second << endl;    }    //.get_allocator()函数声明是:allocator_type get_allocator()const noexcept;    //用于返回和map关联对象的副本;    {        pair<const char,int> *p;        p=mymap2.get_allocator().allocate(5);        auto psize = sizeof(map<char,int>::value_type)*5;        cout << "The allocated array has sizeof " << psize << " bytes" << endl;        mymap2.get_allocator().deallocate(p,5);    }    //.insert()包含的函数声明:    //pair<iterator,bool> insert(const value_type& val);    //template<class P> pair(iterator,bool) insert(P&& val);    //    //iterator insert(const_iterator position,const value_type& val);    //template<class P> iterator insert(const_iterator position,P&& val);    //    //template<class InputIterator>    //void insert(InputIterator first,InputIterator last);    //void insert(initializer_list<value_type> il);    //再进行元素的插入过程中,元素键是唯一的,所以在进行元素插入时,需要进行检查,    //如果元素重复,就不进行插入,迭代器返回现有元素,否则进行元素插入;    //    {        map<char,int> mynewmap;        mynewmap.insert(pair<char,int>('a',101));        mynewmap.insert(pair<char,int>('b',102));        mynewmap.insert(pair<char,int>('c',103));        mynewmap.insert(pair<char,int>('c',104));        mynewmap.insert(pair<char,int>('d',105));        pair<map<char,int>::iterator,bool> ret;        mynewmap.insert(pair<char,int>('b',212));        if(ret.second==false){            cout << "element 'b' has already exist " << endl;        }else {            cout << "elemen 'b' inseret successful " << endl;        }        map<char,int>::iterator it = mynewmap.begin();        mynewmap.insert(it,pair<char,int>('b',300));        mynewmap.insert(it,pair<char,int>('c',200));        map<char,int> anothermap;        anothermap.insert(mynewmap.begin(),mynewmap.find('c'));        cout << "mynewmap contains: ";        for(auto X:mynewmap)            cout << X.first << " " << X.second << " ";        cout << endl;        for(auto X:anothermap)            cout << X.first << " " << X.second << " ";        cout << endl;    }       //.key_comp()用于返回一个用于比较键值的对象的副本;    //.key_compare key_comp()const;    {        map<char,int> mymap;        map<char,int>::key_compare mycomp = mymap.key_comp();        mymap['a']=100;        mymap['b']=101;        mymap['c']=102;        cout << "mymap contains: ";        char highest =mymap.rbegin()->first;        map<char,int>::iterator it = mymap.begin();        do{            cout << it->first << "=>" << it->second << " ";        }while(mycomp((*it++).first,highest));        cout <<'\n';    }    //.lower_bound()包含有两种形式:iterator lower_bound(const key_type& k);    //const_iterator lower_bound(const key_type& k) const;    {        map<char,int> mymap;        map<char,int>::iterator itlow,itup;        mymap['1']=16;        mymap['2']=19;        mymap['3']=20;        mymap['4']=19;        mymap['5']=17;        itlow = mymap.lower_bound('3');        itup = mymap.upper_bound('3');        mymap.erase(itlow,itup);        for(auto X:mymap){            cout << X.first << "=>" << X.second << " ";        }        cout << endl;    }    //.max_size()用于返回当前容器可以存放的最大值;    //size_type max_size() const noexcept;    //    //.operator=:用于实现两个不同的map对象进行赋值;    //map& operator=(const map& x);拷贝    //map& operator=(const map&& x);移动    //map& operator=(initializer_list<value_type> il);初始化列表    {        map<char,int> first;        map<char,int> second;        first['x']=1;        first['y']=2;        first['z']=3;        first['a']=4;        first['b']=5;        cout << "first contains: ";        for(auto X:first)            cout << "[" << X.first << ":" << X.second << " ";        cout << endl;        second = first;        for(auto X:second)            cout << "[" << X.first << ":" << X.second << " ";        cout << endl;        first = map<char,int>();        cout << first.size() << endl;    }    //.mapped_type& operator[](const key_type& k);    //mapped_type& operator[](const key_type&& k);    //.swap()用于快速的交换两个map结构    mymap1.swap(mymap1);    cout << "mymap1 contains: ";    for(auto X:mymap1)        cout << "[" << X.first << ":" << X.second << "] ";    cout << endl;    cout << "mymap2 contains: ";    for(auto X:mymap2)        cout << "[" << X.first << ":" << X.second << "] ";    cout << endl;    //.upper_bound()     //iterator upper_bound(const key_type& k);    //const_iterator upper_bound(const key_type& k)const;    //.value_comp():value_compare value_comp() const;    {        map<char,int> mymap;        mymap['a'] = 1001;        mymap['b'] = 1002;        mymap['c'] = 1003;        auto highest = *mymap.rbegin();        auto it = mymap.begin();        cout << "mymap value contains: ";        do{            cout << it->first << "=>" << it->second << " ";        }while(mymap.value_comp()(*it++,highest));    }    return 0;}