How to Add a Key-Value Pair to a Map in C++ - Step by Step Examples

How to Add a Key-Value Pair to a Map in C++ ?

Answer

To add a key-value pair to a map in C++, you can use the insert method, the subscript operator, or the emplace method.

✐ Examples

1 Adding a Key-Value Pair Using insert Method

We can add a key-value pair to a map in C++ using the insert method, which adds an element with a specific key and value to 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 insert method to add a new key-value pair to the map. The insert method takes a std::pair object, which contains the key and value to be added.
We print the updated map to the console using a range-based for loop and std::cout.

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"}
    };

    // Add a key-value pair using insert method
    myMap.insert(std::pair<int, std::string>(4, "four"));

    // Print the updated map
    for (const auto& pair : myMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

1: one
2: two
3: three
4: four

2 Adding a Key-Value Pair Using Subscript Operator

We can add a key-value pair to a map in C++ using the subscript operator, which adds an element with a specific key and value to 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 subscript operator to add a new key-value pair to the map. The subscript operator allows us to specify the key and assign a value to it.
We print the updated map to the console using a range-based for loop and std::cout.

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"}
    };

    // Add a key-value pair using subscript operator
    myMap[4] = "four";

    // Print the updated map
    for (const auto& pair : myMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

1: one
2: two
3: three
4: four

3 Adding a Key-Value Pair Using emplace Method

We can add a key-value pair to a map in C++ using the emplace method, which constructs an element in place within 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 emplace method to add a new key-value pair to the map. The emplace method takes the key and value as arguments and constructs the element in place.
We print the updated map to the console using a range-based for loop and std::cout.

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"}
    };

    // Add a key-value pair using emplace method
    myMap.emplace(4, "four");

    // Print the updated map
    for (const auto& pair : myMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }

    return 0;
}

Output

1: one
2: two
3: three
4: four

Summary

In this tutorial, we learned How to Add a Key-Value Pair to a Map in C++ language with well detailed examples.

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How to Add a Key-Value Pair to a Map in C++ - Step by Step Examples