STL -- map

時間 2019-11-14

標籤 stl map 简体版

原文原文鏈接

map是C++的一個標準容器，key-record的關係。ios

1. map的構造函數api

map<string, int> mapstring;
map<int, string> mapint;
map<string, char> mapstring;
map<char, string> mapchar;
map<char, int> mapchar;
map<int, char> mapint;

2. map添加數據app

map<int, string> maplive;
maplive.insert(pair<int, string>(102, "active"));
maplive.insert(map<int, string>::value(type(321, "hai"));
maplive[122] = "April";//map中最簡單最經常使用的插入添加

3. map中查找元素函數

find()函數返回一個迭代器指向鍵值爲key的元素，若是沒找到折返回指向map尾部的迭代器spa

map<int ,string >::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;

4. map中元素刪除code

map<int, string>::iterator it;
it = maplive.find(112);
if (it == maplive.end())
    cout<<"we do not find 112"<<endl;
else
    maplive.erase(it);

5. map中swap用法blog

　　map中的swap不是一個容器的元素的交換，而是兩個容器的交換。排序

#include <map>
  #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;
}

6. map中sort問題ci

map中的元素是自動按照key升序排序，因此不能對map用sort函數。get

#include <map>
#include <iostream>

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;
  
}
  The original map m1 is:
  1 20
  2 50
  3 60
  4 40
  6 40
  7 30