C++的map与multimap的使用

map 键-值对的集合，可理解为关联数组。

#include<iostream>#include<map>using namespace std;int main(){    map<string, int> word_cnt;    string word;    /*利用数组下标插入    while(cin >> word){        ++word_cnt[word];    }    */    /*利用insert插入*/    while(cin >> word){        pair<map<string, int>::iterator, int> ret = word_cnt.insert(make_pair(word, 1));        if(!ret.second)            ++ret.first->second;    }    /*erase删除键为June的元素*/    word_cnt.erase("June");    /*迭代遍历*/    map<string, int>::const_iterator it = word_cnt.begin();    while(it != word_cnt.end()){        cout << it->first << " occurs "             << it->second << " times" << endl;        ++it;    }    /*测试数据：June July the on the table the July book*/    /*查找 find count*/    map<string, int>::iterator u = word_cnt.find("the");    //find返回迭代器，若不存在则返回指向末端的迭代器    if(u != word_cnt.end()){        cout << u->first << " occurs "             << u->second << " times" << endl;    }    int cnt = word_cnt.count("July");    //count的返回值是0（容器中不存在）或1（容器中存在），因为map是一个键对应一个值    cout << cnt << endl;}

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multimap 一个键可对应多个值，不能使用下标操作。

#include<iostream>#include<map>using namespace std;int main(){    multimap<string, string> author;    /*用insert添加元素*/    author.insert(make_pair(string("Happy"), string("Hello")));    author.insert(make_pair(string("June"), string("July")));    author.insert(make_pair(string("Happy"), string("Hi")));    author.insert(make_pair(string("Happy"), string("Good")));    /*count(k)返回容器中有k键的元素个数*/    multimap<string, string>::size_type cnt = author.count("Happy");    cout << cnt << endl;    /*find(k)函数返回迭代器*/    multimap<string, string>::iterator c = author.find("Happy");    typedef multimap<string, string>::size_type sz_type;    for(sz_type i = 0; i != cnt; ++i, ++c)        cout << c->second << " ";    /*lower_bound(k)返回不小于k的迭代器，lower_bound(k)返回大于k的迭代器。*/    cout << endl << author.lower_bound("Happy")->second << " "         << author.upper_bound("Happy")->second << endl;    /*equal_range(k)返回存在k键的元素范围的pair类型（左闭右开区间）*/    typedef multimap<string, string>::iterator authors;    pair<authors, authors> k = author.equal_range("Happy");    cout << k.first->second << " "         << k.second->second << endl;}