STL标准库的关联容器

关联容器支持高效的关键字查找和访问。map中的元素是一些关键字-值（key-value）对：关键字起到索引的作用，值则是表示与索引相关联的数据。set中每个元素只包含一个关键字，可以说set是一个特殊的map。

标准库提供8个关联容器，允许重复关键字的容器的名字中都包含单词multi；不保持关键字按顺序存储的容器的名字都以unordered开头。因此一个unordered_multi_set是一个允许重复关键字，元素无序保存的集合。

类型map和multimap定义在头文件map中；set和multiset定义在头文件set中；无序容器则定义在头文件unordered_map和unordered_set中。

先来一个set使用的简单例子：

// set_ex.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <iostream>#include <set>using namespace std;int _tmain(int argc, _TCHAR* argv[]){//set自动排序set<int> myset;multiset<int> mset;for(int i=0; i<10; i++)mset.insert(10-i);mset.insert(7);for(multiset<int>::iterator it=mset.begin(); it!=mset.end();it++){cout<<*it<<" ";}cout<<endl;for(int i=0; i<10; i++){myset.insert(10-i);}myset.insert(5);set<int>::iterator itor,upitor,downitor;for(itor=myset.begin(); itor!=myset.end(); itor++){cout<<*itor<<" ";}cout<<endl;//查询、删除数据int num=5;cout<<"find and delete element "<<num<<endl;itor=myset.find(num);if(itor!=myset.end()){myset.erase(itor);}for(itor=myset.begin(); itor!=myset.end(); itor++){cout<<*itor<<" ";}cout<<endl;//元素边界num=5;upitor=myset.lower_bound(num);downitor=myset.upper_bound(num);cout<<num<<" lower bound is "<<*upitor<<endl;cout<<num<<" upper bound is "<<*downitor<<endl;pair<set<int>::iterator, set<int>::iterator> ret=myset.equal_range(7);cout<<num<<" lower bound is "<<*ret.first<<endl;cout<<num<<" upper bound is "<<*ret.second<<endl;//check数据是否在容器中if(myset.count(num)>0){cout<<num<<" is an element of myset."<<endl;}else{cout<<num<<" is not an element of myset."<<endl;}//输出容器大小cout<<"set size: "<<myset.size()<<endl;for(itor=myset.begin(); itor!=myset.end(); itor++){cout<<*itor<<" ";}cout<<endl;system("pause");return 0;}

一个map使用的简单例子：

// map_ex.cpp : 定义控制台应用程序的入口点。//#include "stdafx.h"#include <iostream>#include <map>using namespace std;int _tmain(int argc, _TCHAR* argv[]){map<char, int> mymap;map<char, int>::iterator itor;pair<map<char, int>::iterator, bool> ret1;pair<map<char, int>::iterator,map<char, int>::iterator> ret;//插入元素mymap['a']=10;mymap['b']=20;mymap['c']=30;mymap['d']=40;ret1=mymap.insert(pair<char, int>('c',500));if(ret1.second==false){cout<<"element 'c' already existed";cout<<" with a value of "<<ret1.first->second<<endl;}//寻找、删除itor=mymap.find('d');mymap.erase(itor);//边界ret=mymap.equal_range('b');cout<<"lower bound points to: ";cout<<ret.first->first<<" => "<<ret.first->second<<endl;cout<<"upper bound points to: ";cout<<ret.second->first<<" => "<<ret.second->second<<endl;//输出容器元素cout<<"mymap contains: ";for(itor=mymap.begin(); itor!=mymap.end(); itor++){cout<<(*itor).first<<" => "<<(*itor).second<<endl;}system("pause");return 0;}

再来一个multimap查找元素的例子

// query.cpp : 定义控制台应用程序的入口点。//在multimap中查找元素#include "stdafx.h"#include <iostream>#include <fstream>#include <string>#include <map>using namespace std;int _tmain(int argc, _TCHAR* argv[]){multimap<string,string> mymap;string path="list.txt";string printpath="print.txt";string text;ifstream file;file.open(path);//读取txt文件while(file){if(getline(file,text)){int n=text.find_first_of(" ");string author=text.substr(0,n);string book=text.substr(n);//向multimap添加元素mymap.insert(make_pair(author,book));}}//利用迭代器打印multimap中的数据cout<<"打印按字母顺序排好的文本，按“作者 著作”排序："<<endl;multimap<string,string>::iterator itor;for(itor=mymap.begin();itor!=mymap.end(); itor++){cout<<(*itor).first<<"  "<<(*itor).second<<endl;}cout<<"********************我是万恶的分割线********************"<<endl;string search_item("jiang");cout<<"打印查找到"<<search_item<<"作者的著作"<<endl;auto entries=mymap.count(search_item);auto copyentries=entries;auto iter=mymap.find(search_item);auto copyiter=iter;while(entries){cout<<iter->first<<"  "<<iter->second<<endl;++iter;--entries;}//复习下文本操作，把上述东西打印到文本ofstream File;File.open(printpath,ios_base::trunc);while(copyentries){File<<copyiter->first<<"  "<<copyiter->second<<endl;++copyiter;--copyentries;}system("pause");return 0;}

结果：