How to Get the Size (Number of Key-Value Pairs) of a Map in C++ - Step by Step Examples

How to Get the Size (Number of Key-Value Pairs) of a Map in C++ ?

Answer

To get the size (number of key-value pairs) of a map in C++, you can use the size() method. This method returns the number of elements in the map.

✐ Examples

1 Getting the Size of a Map Using size() Method

We can get the size of a map in C++ using the size() method, which provides the number of key-value pairs in the map.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare and initialize a map named myMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the size method to get the number of key-value pairs in the map.
We store the size in a variable named mapSize.
We print the size to the console using the std::cout function to verify the number of key-value pairs in the map.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize a map
    std::map<int, std::string> myMap = {
        {1, "one"},
        {2, "two"},
        {3, "three"}
    };

    // Get the size of the map
    size_t mapSize = myMap.size();

    // Print the size
    std::cout << "Size of the map: " << mapSize << std::endl;

    return 0;
}

Output

Size of the map: 3

2 Getting the Size of an Empty Map

We can also get the size of an empty map in C++ using the size() method, which returns 0 when the map is empty.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare an empty map named emptyMap with integer keys and string values.
We use the size method to get the number of key-value pairs in the empty map.
We store the size in a variable named emptyMapSize.
We print the size to the console using the std::cout function to verify that the map is empty.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare an empty map
    std::map<int, std::string> emptyMap;

    // Get the size of the empty map
    size_t emptyMapSize = emptyMap.size();

    // Print the size
    std::cout << "Size of the empty map: " << emptyMapSize << std::endl;

    return 0;
}

Output

Size of the empty map: 0

3 Getting the Size of a Map After Inserting Elements

We can get the size of a map in C++ after inserting elements using the size() method, which provides the updated number of key-value pairs in the map.

For example,

We start by including the <map> and <iostream> header files, which provide the necessary functions and data structures for working with maps and input-output operations.
We declare an empty map named dynamicMap with integer keys and string values.
We insert some key-value pairs into the map using the insert method.
We use the size method to get the number of key-value pairs in the map after insertion.
We store the size in a variable named dynamicMapSize.
We print the size to the console using the std::cout function to verify the updated number of key-value pairs in the map.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare an empty map
    std::map<int, std::string> dynamicMap;

    // Insert elements into the map
    dynamicMap.insert({1, "one"});
    dynamicMap.insert({2, "two"});
    dynamicMap.insert({3, "three"});

    // Get the size of the map after insertion
    size_t dynamicMapSize = dynamicMap.size();

    // Print the size
    std::cout << "Size of the map after insertion: " << dynamicMapSize << std::endl;

    return 0;
}

Output

Size of the map after insertion: 3

Summary

In this tutorial, we learned How to Get the Size (Number of Key-Value Pairs) of a Map in C++ language with well detailed examples.

◀ Previous Next ▶

C++ Tutorials

C++ How-Tos

How to Get the Size (Number of Key-Value Pairs) of a Map in C++ - Step by Step Examples