STL_Container_map

C++中STL库中关于container的map学习笔记

• 说明

  map内部本身就是按序存储的（比如红黑树）。在我们插入<key,value>键值对时，就会按照key的大小顺序进行存储。这也是作为key的类型必须能够进行小于运算比较的原因

• begin()/end()

      map<char,int> mymap;
      map<char,int>::iterator it;
      mymap['a']=100;
      mymap['b']=200;
      mymap['c']=300
        
      for(it=mymap.begin();it<mymap.end();it++)
          cout<< (*it).first << (*it).second<<endl;
        
      //不使用iterator遍历见empty()
  

• clear()

  清空map中的数据

• count()

  查看map中是否存在某个key值,无法定位数据位置

      map<char,int> mymap;
      mymap ['a']=101;
      mymap ['c']=202;
      mymap ['f']=303;
        
      mymap.count('a')  返回1
      mymap.count('x')  返回0
  

• empty()

  返回0 表示空

      //不使用iterator遍历map
       while (!mymap.empty())
       {
           cout << mymap.begin()->first << " => ";
           cout << mymap.begin()->second << endl;
           mymap.erase(mymap.begin());
       }
  

• equal_range()

  lower_bound返回区间A的第一个迭代器，算法upper_bound返回区间A的最后一个元素的下一个位置，算法equal_range则是以pair的形式将两者都返回

    map<char,int> mymap;
    pair<map<char,int>::iterator,map<char,int>::iterator> ret;
  
    mymap['a']=10;
    mymap['b']=20;
    mymap['c']=30;
  
    ret = mymap.equal_range('b');
  
    cout << "lower bound points to: ";
    cout << ret.first->first << " => " << ret.first->second << endl;
    // 'b' => 20
    cout << "upper bound points to: ";
    cout << ret.second->first << " => " << ret.second->second << endl;
    // 'c' =>30
  

• erase()

      map<char,int> mymap;
      map<char,int>::iterator it;
      mymap['a']=10;
      mymap['b']=20;
      mymap['c']=30;
      mymap['d']=40;
      mymap['e']=50;
      mymap['f']=60;
      //按位置删除
      it = mymap.find('b');
      mymap.erase(it);
      //按关键字删除
      mymap.erase('c');
      //按区间删除
      it = mymap.find('e');
      mymap.erase(it,mymap.end());
  

• find()

  查找关键字返回对应位置

      it = find('c');
  

• get_allocator()

      int psize;
      map<char,int> mymap;
      pair<const char,int>* p;
      p = mymap.get_allocator().allocate(5);
        
      psize = (int)sizeof(map<char,int>::value_type)*5; 
      mymap.get_allocator().deallocate(p,5);
  

• insert()

      map<char,int>mymap;
      map<char,int>::iterator it;
      pair<map<char,int>::iterator,bool> ret;
        
      //插入方式1，单个参数
      mymap.insert(pair<char,int>('a',100));
      mymap.insert(pair<char,int>('z',200));
      ret = mymap.insert(pair<char,int>('z',500));//返回false
      //插入方式二,iterator定位
      it = mymap.begin();
      mymap.insert(it,pair<char,int>('b',300));
      mymap.insert(it,pair<char,int>('c',400));
      //插入方式三
      map<char,int> othermap;
      othermap.insert(mymap.begin(),mymap.find('c'));
  

• key_comp()

  关键字比较

      map<char,int>::key_compare mycomp;
      char highest;
      mycomp = mymap.key_comp();
      highest = mymap.rbegin()->first;
      用法：
      it=mymap.begin();
      do {
           cout << (*it).first << " => " << (*it).second << endl;
      } while ( mycomp((*it++).first, highest) );
  

• lower_bound()/up_bound()

  lower_bound:直向当前值

  up_bound:指向当前的下一个值

      map<char,int> mymap;
      map<char,int>::iterator it,itlow,itup;
        
      mymap['a']=20;
      mymap['b']=40;
      mymap['c']=60;
      mymap['d']=80;
      mymap['e']=100;
        
      itlow=mymap.lower_bound ('b');  // itlow points to b
      itup=mymap.upper_bound ('d');   // itup points to e (not d!)
  

• max_size()

  返回map容器所支持的最大元素数量

• operator=

      map<char,int> first;
      map<char,int> second;
        
      first['x']=8;
      first['y']=16;
      first['z']=32;
        
      second=first;          second.size() = 3
      first=map<char,int>();  first.size() = 0
  

• operator[]

      map<char,string> mymap;
      map<char,string>::iterator it;
        
      mymap['a']="an element";
      mymap['b']="another element";
      mymap['c']=mymap['b'];    mymap['c']  也是"another element"
  

• rbegin()/rend()

  反向遍历map

• size()

  返回map中数据条目的数量

• swap()

  两个map之间的数据交换

• value_comp()

        map<char,int> mymap;
        map<char,int>::iterator it;
        pair<char,int> highest;
        
        mymap['x']=1001;
        mymap['y']=2002;
        mymap['z']=3003;
        
        cout << "mymap contains:\n";
        
        highest=*mymap.rbegin();          // last element
        
        it=mymap.begin();
        do {
          cout << (*it).first << " => " << (*it).second << endl;
        } while ( mymap.value_comp()(*it++, highest) );
  

• 自定义compare()函数

      struct CmpByKeyLength {  
        bool operator()(const string& k1, const string& k2) {  
          return k1.length() < k2.length();  
        }  
      };
  
  
      使用：
      map<string,int,CmpByKeyLength>mymap;
      功能：map会按照key关键字的长度进行排序
  

  ​

  ​