STL map usage

Source: Internet
Author: User
STL map usage from: 1. The elements in map is actually a pair.
2. Map keys generally cannot be pointers, such as int * or char *, which may lead to errors. Commonly Used strings are used, and INT is also used.
3. map is an unordered container, while vector is ordered. the so-called ordered disorder means that the elements are not put in a certain order, but randomly stored in a disordered Order (approximately randomly stored after ing ). so there are some efficiency differences during traversal.
4. Check whether the key content is found:
STD: Map <STD: String, record >:: const_iterator citer;
Citer = stdfile. m_map.find (s );
If (citer = stdfile. m_map.end () // if it is not found, it directs to end.
M_vecmorefile.push_back (s );
If the key content is a pointer, the NULL pointer can also be used to determine.
5. traversal:
STD: Map <STD: String, record >:: iterator ITER;
For (iter = m_map.begin (); iter! = M_map.end (); ITER ++)
STD: String S = ITER-> second. filename;
Since the map content can be equivalent to a pair, it is easy to use ITER-> second to get the value.

By the way, you can refer to the following usage:
1 header file
# Include <map>

2 Definitions
Map <string, int> my_Map;
Or typedef map <string, int> MY_MAP;
MY_MAP my_Map;

3. insert data
(1) my_Map ["a"] = 1;
(2) my_Map.insert (map <string, int >:: value_type ("B", 2 ));
(3) my_Map.insert (pair <string, int> ("c", 3 ));
(4) my_Map.insert (make_pair ("d", 4 ));

4. Search for and modify data
(1) int I = my_Map ["a"];
My_Map ["a"] = I;
(2) MY_MAP: iterator my_Itr;
My_Itr.find ("B ");
Int j = my_Itr-> second;
My_Itr-> second = j;
However, note that the key itself cannot be modified unless it is deleted.

5. delete data
(1) my_Map.erase (my_Itr );
(2) my_Map.erase ("c ");
Note that the first case cannot be deleted during iteration. The reason is that the elements cannot be deleted in foreach mode.

6. Iterative data
For (my_itr = my_map.begin (); my_itr! = My_map.end (); ++ my_itr ){}

7. Other Methods
My_map.size () returns the number of elements
My_map.empty () determines whether it is null
My_map.clear () Clear all elements
You can directly assign values and compare values: =,>, >=, <, <= ,! = And so on

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