C++ map的基本操作和使用

  Map是c++的一个标准容器,她提供了很好一对一的关系,在一些程序中建立一个map可以起到事半功倍的效果,总结了一些map基本简单实用的操作!
1. map最基本的构造函数;
  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添加数据;

  map<int ,string> maplive;  
  1.maplive.insert(pair<int,string>(102,”aclive”));
  2.maplive.insert(map<int,string>::value_type(321,”hai”));
  3, maplive[112]=”April”;//map中最简单最常用的插入添加!
3,map中元素的查找:

  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。        

  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中元素的删除:
  如果删除112;
  map<int ,string >::iterator l_it;;
  l_it=maplive.find(112);
  if(l_it==maplive.end())
       cout<<“we do not find 112″<<endl;
  else  maplive.erase(l_it);  //delete 112;
5,map中 swap的用法:
Map中的swap不是一个容器中的元素交换,而是两个容器交换;
For example:
#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的sort问题:
Map中的元素是自动按key升序排序,所以不能对map用sort函数:
For example:
#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
请按任意键继续. . .

7,   map的基本操作函数:
     C++ Maps是一种关联式容器,包含“关键字/值”对
     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末尾的迭代器
     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()       返回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中元素的个数
     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

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