map::size() in C++ 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.

map::size()
In C++, size() function is used to return the total number of elements present in the map.

Syntax:

map_name.size()

Return Value: It returns the number of elements present in the map.

Examples:

Input : map1 = { 
                {1, "India"},
                {2, "Nepal"},
                {3, "Sri Lanka"},
                {4, "Myanmar"}
               }
        map1.size();
Output: 4

Input : map2 = {};
        map2.size();
Output: 0

// C++ program to illustrate
// implementation of size() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Take any two maps
    map<int, string> map1, map2;

    // Inserting values
    map1.insert(make_pair(1, "India"));
    map1.insert(make_pair(2, "Nepal"));
    map1.insert(make_pair(3, "Sri Lanka"));
    map1.insert(make_pair(4, "Myanmar"));

    // Printing the size
    cout << "map1 size: " << map1.size();
    cout << endl;
    cout << "map2 size: " << map2.size();
    return 0;
}

Output:

map1 size: 4
map2 size: 0

Time complexity: Constant i.e. O(1)