C++中map容器的使用说明

C++中map容器提供一个键值对容器,map与multimap差别仅仅在于multiple允许一个键对应多个值.

一.map的说明

1.头文件

#include<map.h>

2.定义方法

(1)map<string,int> m;

(2)typedef map<string,int> M;

    M m;

3.插入数据

(1)m['a'] = 1

(2)m.insert(map<string,int>::value_type("b",2));

(3)m.insert(pair<string,int>("c",3));

(4)m.insert(make_pair<string,int>("d",4));

4.查找数据和修改数据

(1)int i = m["a"];

    m["a"] = i;

(2)m::iterator m_iter;

    m.find("b");

    int j = m_iter->second;

    m_iter->second = j;

!!!注意!!! 键本身是不能被修改的,除非删除.

5.删除数据

(1)m.erase(m_iter);

(2)m.erase("c");

!!!注意!!! 第一种情况在迭代期间是不能被删除的

6   迭代数据 
for   (m_iter=m.begin();   m_iter!=m.end();   ++m_iter)   

{

} 

7   其它方法 
m.size()          返回元素数目 
m.empty()       判断是否为空 
m.clear()         清空所有元素 
可以直接进行赋值和比较：=,   >,   >=,   <,   <=,   !=   等等 

二map的举例

<span style="font-size:18px;">要求: 将mymap中itemstruct的a大于100的项删除  
struct itemstruct 
{ 
     int a; 
     char b[20]; 
}; 
map<string,itemstruct> mymap;</span>

代码1:

<span style="font-size:18px;">#include <iostream> 
#include <ctime> 
#include <map> 
using namespace std; 

typedef struct itemstruct 
{ 
    int a; 
    char b[20]; 
}itemS; 

itemS s[4] = {{102,"what"}, 
             {33,   "hello"}, 
             {198,"world"}, 
             {45,   "c++"} 
             };; 

int main() 
{ 
    map<string,itemS>  mymap; 
    string str[4] = {"1st","2nd","3rd","4th"}; 
    for(int i = 0; i<4; i++) 
    { 
        mymap.insert(make_pair(str[i], s[i])); 
    } 
            
    map<string,itemS>::iterator it; 
    for(it=mymap.begin(); it!=mymap.end(); it++) 
    { 
        if(it->second.a >100)
        { 
        	i=mymap.erase(it);   //----->正确
    		mymap.erase(it);     //----->it失效..
        }
    }
    //first是Key, second是value;
    for(it = mymap.begin();  it!=mymap.end(); it++) 
    { 
        cout<<it->first<<" "<<it->second.a<<" "<<it->second.b<<endl; 
    } 
    system("pause"); 
    return   0; 
}
</span>

代码2:

<span style="font-size:18px;">#include<map> 
#include<iterator> 
#include<string> 
#include<iostream> 
#include<cstring> 
using namespace std; 
struct itemstruct 
{ 
    int   a; 
    char   b[20]; 
    itemstruct(int   t,char*str) 
    { 
    	a=t; 
    	strcpy(b,str); 
    } 
}; 

int main() 
{ 
  
  map<string,itemstruct>mymap; 
  mymap.insert(make_pair("a",itemstruct(10,"hanzhou"))); 
  mymap.insert(make_pair("ab",itemstruct(20,"fuzhou"))); 
  mymap.insert(make_pair("abc",itemstruct(30,"zhengzhou"))); 
  mymap.insert(make_pair("abcd",itemstruct(200,"wuhan"))); 
  mymap.insert(make_pair("abcde",itemstruct(150,"kunming"))); 
  mymap.insert(make_pair("abcdef",itemstruct(50,"xiamen"))); 
  map<string,itemstruct>::iterator   it=mymap.begin(); 

  while(it!=mymap.end()) 
  { 
  	if((it->second).a>100)
  		mymap.erase(it++); 
  	else   
  		it++; 
  }

  it=mymap.begin(); 

  while(it!=mymap.end()) 
  { 
  	cout<<it->first<<"   "<<(it->second).a<<"   "<<(it->second).b<<endl; 
  	it++; 
  } 

  system("PAUSE"); 
  return   0; 
  
 }</span>

代码3:

<span style="font-size:18px;">for(map<string,   itemstruct>::iterator   i   =   mymap.begin();   i   !=   mymap.end();) 
{ 
    if(i->second.a   >   100) 
       i   =   mymap.erase(i); 
    else 
       ++i; 
} </span>