How to Convert a Map to an Array of Keys in C++ - Step by Step Examples

How to Convert a Map to an Array of Keys in C++ ?

Answer

To convert a map to an array of keys in C++, you can use a for loop to iterate over the map and store the keys in a vector. This provides a convenient way to extract all keys from the map.

✐ Examples

1 Converting a Map to an Array of Keys Using a for Loop

We can convert a map to an array of keys in C++ using a for loop, which provides a straightforward way to iterate over all key-value pairs and collect the keys.

For example,

We start by including the <map> and <vector> header files, which provide the necessary functions and data structures for working with maps and vectors.
We also include the <iostream> header for 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 declare a vector named keys to store the keys from the map.
We use a for loop to iterate over the map and add each key to the keys vector using the push_back method.
We print the keys to the console using a range-based for loop and the std::cout function to verify the conversion.

C++ Program

#include <map>
#include <vector>
#include <iostream>

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

    // Declare a vector to store the keys
    std::vector<int> keys;

    // Convert map to an array of keys using a for loop
    for (const auto& pair : myMap) {
        keys.push_back(pair.first);
    }

    // Print the keys
    std::cout << "Keys: ";
    for (const int& key : keys) {
        std::cout << key << " ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Keys: 1 2 3

2 Converting a Map to an Array of Keys Using std::transform

We can also convert a map to an array of keys in C++ using the std::transform algorithm, which provides a more functional programming approach to collecting the keys.

For example,

We start by including the <map>, <vector>, and <algorithm> header files, which provide the necessary functions and data structures for working with maps, vectors, and algorithms.
We also include the <iostream> header for 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 declare a vector named keys to store the keys from the map.
We use the std::transform algorithm to iterate over the map and add each key to the keys vector using a lambda function.
We print the keys to the console using a range-based for loop and the std::cout function to verify the conversion.

C++ Program

#include <map>
#include <vector>
#include <algorithm>
#include <iostream>

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

    // Declare a vector to store the keys
    std::vector<int> keys;
    keys.reserve(myMap.size()); // Reserve space for efficiency

    // Convert map to an array of keys using std::transform
    std::transform(myMap.begin(), myMap.end(), std::back_inserter(keys), 
                   [](const std::pair<int, std::string>& pair) { return pair.first; });

    // Print the keys
    std::cout << "Keys: ";
    for (const int& key : keys) {
        std::cout << key << " ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Keys: 1 2 3

3 Converting a Map to an Array of Keys Using a Range-Based For Loop

We can convert a map to an array of keys in C++ using a range-based for loop, which provides a modern and concise way to iterate over all key-value pairs and collect the keys.

For example,

We start by including the <map> and <vector> header files, which provide the necessary functions and data structures for working with maps and vectors.
We also include the <iostream> header for 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 declare a vector named keys to store the keys from the map.
We use a range-based for loop to iterate over the map and add each key to the keys vector using the push_back method.
We print the keys to the console using another range-based for loop and the std::cout function to verify the conversion.

C++ Program

#include <map>
#include <vector>
#include <iostream>

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

    // Declare a vector to store the keys
    std::vector<int> keys;

    // Convert map to an array of keys using a range-based for loop
    for (const auto& [key, value] : myMap) {
        keys.push_back(key);
    }

    // Print the keys
    std::cout << "Keys: ";
    for (const int& key : keys) {
        std::cout << key << " ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Keys: 1 2 3

Summary

In this tutorial, we learned How to Convert a Map to an Array of Keys in C++ language with well detailed examples.

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How to Convert a Map to an Array of Keys in C++ - Step by Step Examples