Multimap
声明
multimap<string,string> authors;
元素的添加
//adds first element with key Barth authors.insert(make_pair(string(“Barth, John”),string(“Sot-Weed Factor”))); //ok: adds second element with keyBarth authors.insert(make_pair(string(“Barth, John”),string(“Lost in the Funhouse”)));
元素的删除
string search_item(“Kazuo Ishiguro”); //erase all elements with this key; returnsnumber of elements removed multimap<string,string>::size_typecnt=authors.erase(search_item);
查找元素
方法1： find count
//author we’ll look for string search_item(“Alain de Botton”); //how many entries are there for thisauthor typedef multimap<string,string>::size_type sz_type; sz_typeentries=author.count(search_item); //get iterator to the first entry for thisauthor multimap<string,string>::iteratoriter=author.find(search_item); //loop through the number of entries there arefor this author for(sz_type cnt=0; cnt<entries;++cnt, ++iter) cout<<iter->second<<endl;//print each titile
首先调用count确定某作者所写的书籍数目，然后调用find获得指向第一个该键所关联的元素的迭代器。for循环迭代的次数依赖于count返回的值。在特殊情况下，如果count返回0值，则该循环永不执行。
方法2： lower_bound upper_bound
//definitions of authors and search_item asabove
//beg and end denote range of elements for thisauthor
typedef multimap<string,string>::iterator authors_it;
authors_itbeg=authors.lower_bound(search_item),
end=authors.upper_bound(search_item);
//loop through the number of entries there arefor this author
while(beg!=end){
cout<<beg->second<<endl;//printeach title
++beg;
}
在同一个键上调用lower_bound和upper_bound，将产生一个迭代器范围，指示出该键所关联的所有元素。如果该键在容器中存在，则会获得两不同的迭代器：lower_bound返回的迭代器指向该键关联的第一个实例，而upper_bound返回的迭代器则指向最后一个实例的下一位置。如果该键不在multimap中，这两个操作将返回同一个迭代器，指向依据元素的排列顺序该键应该插入的位置。
方法3： equal_range
//definitions of authors and search_item asabove
//pos holds iterators that denote range ofelements ofr this key
pair<authors_it,authors_it>pos=authors.equal_range(search_item);
//loop through the number of entries there arefor this author
while(pos.first!=pos.second){
cout<<pos.first->second<<endl;//printeach titile
++pos.first;
}
pair对象的first成员存储lower_bound函数返回的迭代器，而second成员则记录upper_bound函数返回的迭代器。
#include <iostream>
#include <string>
#include <map>
using namespace std;
typedef struct employee
{
//Member Function
public:
employee(long eID, string e_Name, floate_Salary);
//Attribute
public:
longID; //Employee ID
stringname; //Employee Name
floatsalary; //Employee Salary
}employee;
//创建multimap的实例，整数(职位编号)映射员工信息
typedef multimap<int, employee>EMPLOYEE_MULTIMAP;
typedef multimap<int,employee>::iteratorEMPLOYEE_IT; //随机访问迭代器类型
typedef multimap<int,employee>::reverse_iteratorEMPLOYEE_RIT; //反向迭代器类型
employee::employee(long eID, string e_Name, floate_Salary)
: ID(eID), name(e_Name), salary(e_Salary) {}
//函数名：output_multimap
//函数功能：正向输出多重映射容器里面的信息
//参数：一个多重映射容器对象
void output_multimap(EMPLOYEE_MULTIMAP employ)
{
EMPLOYEE_IT employit;
for (employit = employ.begin(); employit !=employ.end(); employit++)
{
cout <<(*employit).first << '\t'<< (*employit).second.ID
<< '\t'<< (*employit).second.name<< '\t'<< (*employit).second.salary
<< '\t'<< endl;
}
}
//函数名：reverse_output_multimap
//函数功能：逆向输出多重映射容器里面的信息
//参数：一个多重映射容器对象
void reverse_output_multimap(EMPLOYEE_MULTIMAP employ)
{
EMPLOYEE_RIT employit;
for (employit = employ.rbegin(); employit !=employ.rend(); employit++)
{
cout <<(*employit).first << '\t'<< (*employit).second.ID
<< '\t'<< (*employit).second.name<< '\t'<< (*employit).second.salary
<< '\t'<< endl;
}
}
int main(int argc, char *argv[])
{
EMPLOYEE_MULTIMAPemployees; //多重映射容器实例
//下面四个语句分别构造一个员工对象插入到多重映射容器
//注意因为是多重映射，所以可以出现重复的键，例如下面的信息有两个职位编号为118的员工
employees.insert(EMPLOYEE_MULTIMAP::value_type(118, employee(100,"luojiafeng", 8000)));
employees.insert(EMPLOYEE_MULTIMAP::value_type(112, employee(101,"luojiahui", 6000)));
employees.insert(EMPLOYEE_MULTIMAP::value_type(113, employee(102,"luokaifeng", 10000)));
employees.insert(EMPLOYEE_MULTIMAP::value_type(118, employee(103,"xujinghua", 20000)));
//正序输出多重映射容器中的信息
cout << "职位编号"<< "员工ID"<< '\t'
<< "姓名"<< '\t'<< '\t'<< "工资"<< endl;
output_multimap(employees);
//逆序输出多重映射容器中的信息
cout << "职位编号"<< "员工ID"<< '\t'
<< "姓名"<< '\t'<< '\t'<< "工资"<< endl;
reverse_output_multimap(employees);
//输出容器内的记录条数
cout<< "共有"<< employees.size()<< "条员工记录"<< endl;
return 0;
}