20160804-CPP-map

map def: Constructs a list of a specific size or with elements of a specific value or with a specific allocator or as a copy of some other map.

1、map之间可以用 = 或者 ! = 来比较两个map之间是否相等， multimap也可以用。

map和multimap的区别

http://blog.youkuaiyun.com/cws1214/article/details/8211881

2、multimap <int, int> m1, m2, m3;

3、map之间也可以用<=, <, >=, > 

The less-than relationship between two objects is based on a comparison of the first pair of unequal elements.

4、swap( m1, m3 )
Exchanges the elements of two maps or multimaps.

关键的私有值

一个是key，用key来索引data value

有用的成员函数

5、at的使用 

map<char, int> Mymap; 

Mymap c1; 

c1.insert(value_type('a', 1));

cout << "c1.at('a') == " << c1.at('a') <<endl; 

6、begin()的使用

Returns an iterator that points to the first element in the map.

7、find()的使用

template <typename C, class T> void findit(const C& c, T val) {
    cout << "Trying find() on value " << val << endl;
    auto result = c.find(val);
    if (result != c.end()) {
        cout << "Element found: "; print_elem(*result); cout << endl;
    } else {
        cout << "Element not found." << endl;
    }
}
8、max_size()

 
max_size
Returns
 the maximum length of the map.
9. size()

 
size
Returns
 the number of elements in the map.
10、[ ]

// Insert a data value of 10 with a key of 1
   // into a map using the operator[] member function
   m1[ 1 ] = 10;