Map in C++ Standard Template Library (STL)

Maps are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have same key values.

 
Some basic functions associated with Map:
begin() – Returns an iterator to the first element in the map
end() – Returns an iterator to the theoretical element that follows last element in the map
size() – Returns the number of elements in the map
max_size() – Returns the maximum number of elements that the map can hold
empty() – Returns whether the map is empty
pair insert(keyvalue, mapvalue) – Adds a new element to the map
erase(iterator position) – Removes the element at the position pointed by the iterator
erase(const g)– Removes the key value ‘g’ from the map
clear() – Removes all the elements from the map



 

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#include <iostream>
#include <iterator>
#include <map>
  
using namespace std;
  
int main()
{
  
    // empty map container
    map<int, int> gquiz1;
  
    // insert elements in random order
    gquiz1.insert(pair<int, int>(1, 40));
    gquiz1.insert(pair<int, int>(2, 30));
    gquiz1.insert(pair<int, int>(3, 60));
    gquiz1.insert(pair<int, int>(4, 20));
    gquiz1.insert(pair<int, int>(5, 50));
    gquiz1.insert(pair<int, int>(6, 50));
    gquiz1.insert(pair<int, int>(7, 10));
  
    // printing map gquiz1
    map<int, int>::iterator itr;
    cout << "\nThe map gquiz1 is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = gquiz1.begin(); itr != gquiz1.end(); ++itr) {
        cout << '\t' << itr->first
             << '\t' << itr->second << '\n';
    }
    cout << endl;
  
    // assigning the elements from gquiz1 to gquiz2
    map<int, int> gquiz2(gquiz1.begin(), gquiz1.end());
  
    // print all elements of the map gquiz2
    cout << "\nThe map gquiz2 after"
         << " assign from gquiz1 is : \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
        cout << '\t' << itr->first
             << '\t' << itr->second << '\n';
    }
    cout << endl;
  
    // remove all elements up to
    // element with key=3 in gquiz2
    cout << "\ngquiz2 after removal of"
            " elements less than key=3 : \n";
    cout << "\tKEY\tELEMENT\n";
    gquiz2.erase(gquiz2.begin(), gquiz2.find(3));
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
        cout << '\t' << itr->first
             << '\t' << itr->second << '\n';
    }
  
    // remove all elements with key = 4
    int num;
    num = gquiz2.erase(4);
    cout << "\ngquiz2.erase(4) : ";
    cout << num << " removed \n";
    cout << "\tKEY\tELEMENT\n";
    for (itr = gquiz2.begin(); itr != gquiz2.end(); ++itr) {
        cout << '\t' << itr->first
             << '\t' << itr->second << '\n';
    }
  
    cout << endl;
  
    // lower bound and upper bound for map gquiz1 key = 5
    cout << "gquiz1.lower_bound(5) : "
         << "\tKEY = ";
    cout << gquiz1.lower_bound(5)->first << '\t';
    cout << "\tELEMENT = "
         << gquiz1.lower_bound(5)->second << endl;
    cout << "gquiz1.upper_bound(5) : "
         << "\tKEY = ";
    cout << gquiz1.upper_bound(5)->first << '\t';
    cout << "\tELEMENT = "
         << gquiz1.upper_bound(5)->second << endl;
  
    return 0;
}

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Output:

The map gquiz1 is : 
    KEY    ELEMENT
    1    40
    2    30
    3    60
    4    20
    5    50
    6    50
    7    10


The map gquiz2 after assign from gquiz1 is : 
    KEY    ELEMENT
    1    40
    2    30
    3    60
    4    20
    5    50
    6    50
    7    10


gquiz2 after removal of elements less than key=3 : 
    KEY    ELEMENT
    3    60
    4    20
    5    50
    6    50
    7    10

gquiz2.erase(4) : 1 removed 
    KEY    ELEMENT
    3    60
    5    50
    6    50
    7    10

gquiz1.lower_bound(5) :     KEY = 5        ELEMENT = 50
gquiz1.upper_bound(5) :     KEY = 6        ELEMENT = 50

 

List of all functions of Map:

 
Recent articles on Map

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