C++map用法

C++ map用法

C++ 中 map 提供的是一种键值对容器,里面的数据都是成对出现的,如下图:每一对中的第一个值称之为关键字(key),每个关键字只能在 map 中出现一次;第二个称之为该关键字的对应值。在一些程序中建立一个 map 可以起到事半功倍的效果,本文为大家总结了 map 的一些基本简单的操作! 

Map的使用

    需要导入头文件#include <map> // STL头文件没有扩展名.h

map 对象是一个模版类,需要关键字和存储对象两个模版参数 std::map<int , std::string> person;

可以对模版进行类型定义使其使用方便typedef std::map<int , std::string> MAP_INI_STRING;

MAP_INI_STRING person;

Map 的构造1、map 最基本的构造函数;

    std::map<int , std::string> mapPerson;

2、map 添加数据;1) insert 函数插入 pair 数据std::map < int , std::string > mapPerson;

mapPerson.insert(pair < int,string > (1,"Jim"));2)insert 函数插入 value_type 数据mapPerson.insert(std::map < int, std::string > ::value_type (2, "Tom"));3)用数组方式插入数据mapPerson[3] = "Jerry";

    3、Map 数据的遍历三种最常用的遍历方法:1)前向迭代器std::map &lt; int ,std::string &gt; ::iterator it;

    std::map < int ,std::string > ::iterator itEnd;

    it = mapPerson.begin();

    itEnd = mapPerson.end();

    while (it != itEnd) {

cout<<it->first<<' '<<it->second<<endl;

it++;

}2)反向迭代器std::map < int, string > ::reverse_iterator iter;

for(iter = mapPerson.rbegin(); iter != mapPerson.rend(); iter++)

cout<<iter->first<<" "<<iter->second<<endl;

3)数组形式mapPerson.insert(std::map<int, std::string>::value_type (1, "Tom"));

mapPerson[2] = "Jim";

mapPerson[3] = "Jerry";

int nSize = mapPerson.size();

for(int n = 1; n <= nSize; n++)

qDebug()<<QString::fromStdString(mapPerson[n]);三种都是遍历,建议使用前向迭代器,慎用使用数组形成(角标开始位置谨慎)。

4、map 中元素的查找:

    &nbsp;&nbsp;&nbsp;find() 函数返回一个迭代器指向键值为 key 的元素,如果没找到就返回指向 map 尾部的迭代器。&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; map&lt;int ,string &gt; ::iterator l_it;; 

l_it = maplive.find(112);

if(l_it == maplive.end())

cout<<"we do not find 112"<<endl;

else cout<<"wo find 112"<<endl;

    5、map 中元素的删除:

&nbsp;&nbsp;&nbsp;如果删除 112;iterator erase(iterator it) ;//通过一个条目对象删除

iterator erase(iterator first,iterator last); //删除一个范围

size_type erase(const Key&key); //通过关键字删除

clear();//就相当于enumMap.erase(enumMap.begin(),enumMap.end());

    6、map 中&nbsp;swap 的用法:

&nbsp;&nbsp;Map 中的 swap 不是一个容器中的元素交换,而是两个容器交换;

&nbsp;&nbsp;示例: #include &lt;map&gt;

include <iostream>

using namespace std;

int main( )

{

map < int, int > m1, m2, m3;

map < int, int >::iterator m1_Iter;

m1.insert ( pair < int, int > ( 1, 10 ) );

m1.insert ( pair < int, int > ( 2, 20 ) );

m1.insert ( pair < int, int > ( 3, 30 ) );

m2.insert ( pair < int, int > ( 10, 100 ) );

m2.insert ( pair < int, int > ( 20, 200 ) );

m3.insert ( pair < int, int > ( 30, 300 ) );

cout << "The original map m1 is:";

for ( m1_Iter = m1.begin( ); m1_Iter != m1.end( ); m1_Iter++ )

cout << " " << m1_Iter->second;

cout << "." << endl;

// This is the member function version of swap

//m2 is said to be the argument map; m1 the target map

m1.swap( m2 );

cout << "After swapping with m2, map m1 is:";

for ( m1_Iter = m1.begin( ); m1_Iter != m1.end( ); m1_Iter++ )

cout << " " << m1_Iter -> second;

cout << "." << endl;

cout << "After swapping with m2, map m2 is:";

for ( m1_Iter = m2.begin( ); m1_Iter != m2.end( ); m1_Iter++ )

cout << " " << m1_Iter -> second;

cout << "." << endl;

// This is the specialized template version of swap

swap( m1, m3 );

cout << "After swapping with m3, map m1 is:";

for ( m1_Iter = m1.begin( ); m1_Iter != m1.end( ); m1_Iter++ )

cout << " " << m1_Iter -> second;

cout << "." << endl;

}

    7、map 的 sort 问题:

&nbsp;&nbsp;Map 中的元素是自动按 key 升序排序,所以不能对 map 用 sort 函数:

&nbsp;&nbsp;示例: #include &lt;map&gt; #include &lt;iostream&gt;

using namespace std;

int main( )

{

map < int, int > m1;

map < int, int >::iterator m1_Iter;

m1.insert ( pair < int, int > ( 1, 20 ) );

m1.insert ( pair < int, int > ( 4, 40 ) );

m1.insert ( pair < int, int > ( 3, 60 ) );

m1.insert ( pair < int, int > ( 2, 50 ) );

m1.insert ( pair < int, int > ( 6, 40 ) );

m1.insert ( pair < int, int > ( 7, 30 ) );

cout << "The original map m1 is:"<<endl;

for ( m1_Iter = m1.begin( ); m1_Iter != m1.end( ); m1_Iter++ )

cout << m1_Iter->first<<" "<<m1_Iter->second<<endl;

}

    8、map 的基本操作函数:

&nbsp; &nbsp; C++&nbsp;Maps 是一种关联式容器,包含“关键字/值”对

&nbsp; &nbsp; begin()&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回指向 map 头部的迭代器

&nbsp; &nbsp; clear()&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;删除所有元素

&nbsp; &nbsp; count()&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;返回指定元素出现的次数

&nbsp; &nbsp; empty()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;如果 map 为空则返回 true

&nbsp; &nbsp; end()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;返回指向 map 末尾的迭代器

&nbsp; &nbsp; equal_range()&nbsp; &nbsp; &nbsp; &nbsp; 返回特殊条目的迭代器对

&nbsp; &nbsp; erase()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;删除一个元素

&nbsp; &nbsp; find()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;查找一个元素

&nbsp; &nbsp; get_allocator()&nbsp; &nbsp; &nbsp; 返回map的配置器

&nbsp; &nbsp; insert()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 插入元素

&nbsp; &nbsp; key_comp()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 返回比较元素key的函数

&nbsp; &nbsp; lower_bound()&nbsp; &nbsp; &nbsp;返回键值&gt;=给定元素的第一个位置

&nbsp; &nbsp; max_size()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 返回可以容纳的最大元素个数

&nbsp; &nbsp; rbegin()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 返回一个指向map尾部的逆向迭代器

&nbsp; &nbsp; rend()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;返回一个指向map头部的逆向迭代器

&nbsp; &nbsp; size()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; 返回map中元素的个数

&nbsp; &nbsp; swap()&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;交换两个map

&nbsp; &nbsp; upper_bound()&nbsp; &nbsp; 返回键值&gt;给定元素的第一个位置

&nbsp; &nbsp; value_comp()&nbsp; &nbsp; &nbsp; &nbsp;返回比较元素value的函数