STL中map容器的一點點用法
1. map最基本的建構函式;
map<string ,int>mapstring; map<int,string >mapint;
map<sring,char>mapstring; map< char ,string>mapchar;
map<char,int>mapchar; map<int ,char>mapint;
2. map新增資料;
map<int ,string>maplive;
1. maplive.insert(pair<int,string>(102,"aclive"));
2. maplive.insert(map<int,string>::value_type
3. maplive[112]="April";//map中最簡單最常用的插入新增!
3. map中元素的查詢:
find()函式返回一個迭代器指向鍵值為key的元素,如果沒找到就返回指向map尾部的迭代器。
map<int ,string >::iteratorl_it;;
l_it=maplive.find(112);//返回的是一個指標
if(l_it==maplive.end())
cout<<"we do not find112"<<endl;
elsecout<<"wo find112"<<endl;
map<string,string>m;
if(m[112]=="")
cout<<"we do not find112"<<endl;
4. map中元素的刪除:
如果刪除112;
map<int ,string>::iterator l_it;;
l_it =maplive.find(112);
if( l_it == maplive.end())
cout<<"we do not find112"<<endl;
else maplive.erase(l_it);//delete 112;
5. map中 swap的用法:
Map中的swap不是一個容器中的元素交換,而是兩個容器交換;
For example:
#include<map>
#include<iostream>
usingnamespace 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 m1is:";
for ( m1_Iter = m1.begin( ) ; m1_Iter != m1.end() ; m1_Iter++ )
cout << " "<<m1_Iter->second;
cout << "."<< endl;
// This isthe member function version of swap
// m2 is said to be theargument map; m1 the target map
m1.swap( m2);
cout << "Afterswapping 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, mapm2 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 << "Afterswapping with m3, map m1 is:";
for ( m1_Iter = m1.begin( ); m1_Iter != m1.end(); m1_Iter++ )
cout << " "<< m1_Iter ->second;
cout << "."<< endl;
}
6. map的sort問題:
Map中的元素是自動按key升序排序,所以不能對map用sort函式:
For example:
#include<map>
#include<iostream>
usingnamespace 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 m1is:"<<endl;
for ( m1_Iter = m1.begin( );m1_Iter != m1.end( ); m1_Iter++ )
cout << m1_Iter->first<<""<<m1_Iter->second<<endl;
}
The original map m1 is:
1 20
2 50
3 60
4 40
6 40
7 30
7. map的基本操作函式:
C++Maps 是一種關聯式容器,包含“關鍵字/值”對
begin() 返回指向map頭部的迭代器
clear() 刪除所有元素
count() 返回指定元素出現的次數
empty() 如果map為空則返回true
end() 返回指向map末尾的迭代器
equal_range() 返回特殊條目的迭代器對
erase() 刪除一個元素
find() 查詢一個元素
get_allocator() 返回map的配置器
insert() 插入元素
key_comp() 返回比較元素key的函式
lower_bound() 返回鍵值>=給定元素的第一個位置
max_size() 返回可以容納的最大元素個數
rbegin() 返回一個指向map尾部的逆向迭代器
rend() 返回一個指向map頭部的逆向迭代器