学步园

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;
}