C ++ Primer (fifth edition) Study Notes _ 8_standard template library _ map ing container, _ 8_map

C ++ Primer (fifth edition) Study Notes _ 8_standard template library _ map ing container, _ 8_map

C ++ Primer (fifth edition) Study Notes _ 8_standard template library _ map ing container

The element data of the map ing container is composed of a key value and a ing data. The key value and the ing data have a one-to-one ing relationship.
The data structure of the map ing container is also implemented using the red/black tree.

1. map creation, element insertion, and traversal access

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; int main () {map <string, float> str; // insert an element, key values are in the red/black tree from small to large. str ["Jack"] = 98.5; str ["Bomi"] = 96.0; str ["Kate"] = 97.5; for (map <string, float >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; return 0 ;}

Running result:
Bomi: 96
Jack: 98.5
Kate: 97.5


2. Delete elements and repeated inserted values: erase () and clear () Methods
(1) Like the set container, map maps the erase () function of the container to delete all elements on a key value. You can also use the clear () method to clear the map ing container.
(2) For values inserted repeatedly, only the last inserted value is used.

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; int main () {map <int, char> str; // insert an element, key values are in the red/black tree from small to large. str [25] = 'M'; str [28] = 'K'; str [10] = 'X '; str [30] = 'a'; str [25] = 'I'; // repeat the inserted value, using the last inserted value str [10] = 'y '; // repeat the inserted value, using the last inserted value cout <"original data:" <endl; for (map <int, char >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; // Delete the int n = str element whose key value is 0. erase (0); cout <"Number of deleted elements:" <n <endl; // Delete element n = str whose key value is 25. erase (25); cout <"Number of deleted elements:" <n <endl; cout <"erase () data:" <endl; for (map <int, char >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; str. clear (); cout <"clear () data:" <endl; for (map <int, char >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; return 0 ;}

Running result:
Raw data:
10: y
25: I
28: k
30:
Number of deleted elements: 0
Number of deleted elements: 1
Data after erase:
10: y
28: k
30:
Clear () data:


3. Reverse element traversal: reverse_iterator
The rbegin () and rend methods are required to indicate the start position and end position of reverse traversal.

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; int main () {map <int, char> str; // insert an element, key values are in the red/black tree from small to large. str [25] = 'M'; str [28] = 'K'; str [10] = 'X '; str [30] = 'a'; for (map <int, char >:: reverse_iterator iter = str. rbegin (); iter! = Str. rend (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; return 0 ;}

Running result:
30:
28: k
25: m
10: y


4. Search for elements: find ()
Like set, use the find () method to search for a key value and find the iterator where the return key value is located. Otherwise, the end () iterator position is returned. Because of the red/black tree structure, the search speed is extremely fast.

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; int main () {map <int, char> str; // insert an element, key values are in the red/black tree from small to large. str [25] = 'M'; str [28] = 'K'; str [10] = 'X '; str [30] = 'a'; map <int, char >:: iterator iter; iter = str. find (28); if (iter! = Str. end () cout <(* iter ). first <":" <(* iter ). second <endl; else cout <"not found it" <endl; return 0 ;}

Running result:
28: k


5. Custom comparison functions
By default, elements are inserted in the ascending order of key values. Because the internal data structure is a red/black tree, the comparison function is consistent with the set function. There are two writing methods,
(1) If the element is not a struct, You can compile a comparison function. The following describes how to insert elements into the map in the ascending order of key values:

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; struct myComp {bool operator () (const int & a, const int & B) {return a> B ;}}; int main () {// Insert the element. Place the key value from large to small into the red/black tree map <int, char, myComp> str; str [25] = 'M'; str [28] = 'K'; str [10] = 'X'; str [30] = 'a '; for (map <int, char, myComp >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) cout <(* iter ). first <":" <(* iter ). second <endl; return 0 ;}

Running result:
Running result:
30:
28: k
25: m
10: x


(2) If the element is a struct, you can directly write the comparison function in the struct.

# Include <iostream> # include <stdio. h >#include <vector >#include <map> # include <string> using namespace std; struct Info {string name; float score; // you must write an overloaded function, reload the "<" operator and customize the sorting rule bool operator <(Info a) const {// sort by score from large to small. If you want to sort data from small to large, use the ">" sign. return. score <score ;}}; int main () {// insert an element. The key value ranges from large to small and is placed in the red/black tree. map <Info, int> str; Info info; info. name = "Jack"; info. score = 60; str [info] = 25; info. name = "Bomi"; info. score = 80; str [info] = 10; info. name = "Peti"; info. score = 66.5; str [info] = 30; for (map <Info, int >:: iterator iter = str. begin (); iter! = Str. end (); iter ++) {cout <(* iter ). second <":"; cout <(* iter ). first ). name <"" <(* iter ). first ). score <endl;} return 0 ;}

Running result:
10: Bomi 80
30: Peti 66.5
25: Jack 60


6. map writing for character ing numbers
It is time-consuming to separate the numbers and use the remainder mathematical operation. Using numbers as strings and map ing makes it easy to separate numbers.

# Include <iostream> # include <stdio. h> # include <vector> # include <map> # include <string> using namespace std; int main () {// insert an element, put the key value from big to small into the red/black tree map <char, int> str; str ['0'] = 0; str ['1'] = 1; str ['2'] = 2; str ['3'] = 3; str ['4'] = 4; str ['5'] = 5; str ['6'] = 6; str ['7'] = 7; str ['8'] = 8; str ['9'] = 9; /* // The preceding value assignment statement can be simplified with the loop code for (int j = 0; j <10; j ++) m ['0' + j] = j; */string a; a = "6234"; int sum = 0; for (int I = 0; I <. length (); I ++) sum + = str [a [I]; cout <"sum of each number:" <sum <endl; sum = str [a [0]; for (int I = 1; I <. length (); I ++) {sum * = 10; sum + = str [a [I];} cout <"string converted to a number: "<sum <endl ;}

Running result:
Sum of numbers: 15
String to number: 6234


7. map Writing of digit ing characters

# Include <iostream> # include <stdio. h> # include <vector> # include <map> # include <string> using namespace std; int main () {// insert an element, put the key value from large to small into the red/black tree map <int, char> str; str [0] = '0'; str [1] = '1 '; str [2] = '2'; str [3] = '3'; str [4] = '4'; str [5] = '5 '; str [6] = '6'; str [7] = '7'; str [8] = '8'; str [9] = '9 '; /* // The preceding value assignment statement can be simplified with the loop code for (int j = 0; j <10; j ++) m [j] = '0' + j; */int n = 7; string single; cout < "Convert the unit number to a string:" <single + str [n] <endl; int num = 6234; string s; for (int I = num; I! = 0; I/= 10) {s. insert (s. begin (), str [I % 10]);} cout <"Multi-digit conversion to string:" <s <endl; return 0 ;}

Running result:
Convert unit number to string: 7
Multi-digit conversion to string: 6234

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