STL -- map

map是C++的一个标准容器，key-record的关系。

1. map的构造函数

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添加数据

map<int, string> maplive;
maplive.insert(pair<int, string>(102, "active"));
maplive.insert(map<int, string>::value(type(321, "hai"));
maplive[122] = "April";//map中最简单最常用的插入添加

3. map中查找元素

find()函数返回一个迭代器指向键值为key的元素，如果没找到折返回指向map尾部的迭代器

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中元素删除

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

　　map中的swap不是一个容器的元素的交换，而是两个容器的交换。

#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问题

map中的元素是自动按照key升序排序，所以不能对map用sort函数。

#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

7. map中基本操作函数

begin()返回指向map头部的迭代器

clear()删除所有元素

count()返回指定元素出现的次数

empty()如果map为空则返回true

end()返回指向map尾部的迭代器

equal_range()返回特殊条目的迭代器对

erase()删除一个元素

find()查找一个元素

get_allocator()返回map的配置器

insert()插入元素

key_comp()返回比较元素key的函数

lower_bound()返回键值>=给定元素的第一个位置

max_size()可以容纳的最大元素个数

rbegin()返回一个指向map尾部的逆向迭代器

rend()返回一个指向map头部的逆向迭代器

size()返回map中元素个数

swap()交换两个map

upper_bound()返回键值>给定元素的第一个位置

value_comp()返回比较元素value的函数