STL 关联容器

关联容器的定义
STL中的关联容器有map、multimap、set、multiset。<是默认的比较运算符，但可能有个比较函数参数。这些容器提供了双向迭代器。
Map类存储（键，值）时，他们按照唯一的键来排序。Pair在<utility>中定义。Map的一个有效地功能是可使用运算符[]通过其键来建立下标。由于下标功能在map中提供，所以值可以通过insert函数输入到map中，还可以通过数组类型的赋值来输入，例如下面的语句：Month["December"]=31;
Map类的部分规范如下：

Template<class Key,class T,class Compare=less<Key>> class map { public: explicit map(const Compare &cmp=Compare()); //Default constructor //Precondition :none //postcondition :the map object is initialized to be empty //the default comparison operator is < //A comparision function object may be supplied template<class InputIter> map(InputIter first,InputIter last, const Compare &comp=Compare()); //Constructor :map is initialized with length last-first //and filled with all values from the derefenced //input iterators on the range[first,last]. //precondition :none; //Postcondition :the map contains input itertors in the //range[first,last].if a function comp is supplied,it //is used to compare elements of the map bool empty()const; //determines whether the map is empty //precondition :none //postcondition :Returns true if the map is empty //otherwise returns false size_type size()const; //Determines the size of the map //the returns type size_type is an integral type //precondition :none; //Postcondition :returns the number of elements Iter insert(const value_type &e); Iter insert(Iter i,const value_type &e); //inserts element pair e into the map if a value_type //with the same key is not already present in the map //Takes an optional iterator parameter as a hint as to //where to insert //precondition :the iterator is initialized; //postcondition :Element e has been inserted into the map //and an iterator to e is returned. Iter erase(Iter i); //removes the map element pointed to by iterator i //precondition :none //postcondition :return an iterator pointing to the map //element folling by removed pair. //if the pair was the last element ,the value returned by //end() was returned void erase(Iter first,Iter last); //removes all elements in the range[first,last] //precondition :none //postcondition :the map has no elements in the rang[first,last]; Iter find(const Key_value &e)const; //returns an iterator points to the element //equal to e. //precondition :none //postcondition :if the element is in the map ,an iterator //returned pointing to e; otherwise the value returned by //end() was returned size_type count(const Key_value &e)const; //returns number of elements equal to e, //precondition :none //postcondition :returns number of element equal to //e .since a map has unique keys,count will always //return 1 or 0; Iter lower_bound(const Key_value &e)const; //returns an iterator that points to the first //key that is equal to or greater than e //precondition:none //postcondition :return the comparison function object for //the set//???? Iter upper_bound(const Key_value &e)const; //returns an iterator that points to the first key //that is greater than e; //precondition :none //postcondition :returns the comparison function object for //the set void swap(map<key,T,Compare> &m); //Exchange maps //precondition :none //postcondition :Exchange the contents of the map //m with current map,*this Iter begin(); //returns an iterator to the first element in the map //precondition :none //postcondition :if the map was empty ,the value returned //by end() was returned. Iter end(); //returns an iterator to test for the end of the map //precondition :none //postcondition :the value for the end of the map //was returned. };

注意关联容器有自己的find和count函数来查找数据项。他们还可以使用lower_bound、
upper_bound 和equal_range函数返回一组相等的数据项。数据项使用insert函数添加到关联容器中。对于map和multimap，元素还可以使用下标运算符[]插入。
Multimap和multiset容器类似于对应的map和set，但他们允许键重复。当键可能有两个与它有关的值时，这是很有效的。下面的程序创建了一个map ，然后创建了一个multimap，把姓名存储为键，电话号码存储为值。multimap可以为一个姓名存储对个电话号码，而map会用同一个键覆盖另一个项目。

#include<utility> #include<map> #include<iostream> #include<string> using namespace std; int main() { //declare a map to contain names and phone numbers map<string,string> phoneBook ; //declare a map iterator map<string ,string>::const_iterator it1; string name1="Smith, John"; string name2="Thonpson, Julia"; string name3="Johnson, Mary"; string name4="Little, Carol"; string name5="Johnson, Mary"; string phone1="212-555-444"; string phone2="806-555-6565"; string phone3="445-555-7111"; string phone4="745-555-6787"; string phone5="745-555-7777"; //assign elements to map using subscripts phoneBook[name1]=phone1; phoneBook[name2]=phone2; phoneBook[name3]=phone3; phoneBook[name4]=phone4; phoneBook[name5]=phone5; //print map elements for(it1=phoneBook.begin();it1!=phoneBook.end();it1++) cout<<it1->first<<"\t"<<it1->second<<endl; it1=phoneBook.find(string(name3)); //display found map element if(it1!=phoneBook.end()) cout<<" search for "<<it1->first<<"--phone numbers"<< endl<<it1->second<<endl<<endl; //create a multimap to contain names and phone numbers //using the mak pair function insert elements multimap<string,string> phoneBook2; phoneBook2.insert(make_pair(name1,phone1)); phoneBook2.insert(make_pair(name2,phone2)); phoneBook2.insert(make_pair(name3,phone3)); phoneBook2.insert(make_pair(name4,phone4)); phoneBook2.insert(make_pair(name5,phone5)); typedef multimap<string,string>::const_iterator Iter; Iter it2; for(it2=phoneBook2.begin();it2!=phoneBook2.end();++it2) { cout<<it2->first<<'\t'<<it2->second<<endl; } //return map pairs with the same key pair<Iter,Iter>phoneNum=phoneBook2.equal_range(name3); //display pairs with the same key cout<<" Search for"<<name3<<"--phone numbers:"<<endl; for(it2=phoneNum.first;it2!=phoneNum.second;++it2) cout<<it2->second<<endl; return 0; }