How to Copy a Map in C++ - Step by Step Examples

How to Copy a Map in C++ ?

Answer

To copy a map in C++, you can use the copy constructor or the assignment operator to create a new map that contains the same key-value pairs as the original map. This method provides a straightforward way to duplicate a map.

✐ Examples

1 Copying a Map Using the Copy Constructor

We can copy a map in C++ using the copy constructor, which creates a new map with the same key-value pairs as the original map.

For example,

We start by including the <map> header file, which provides the necessary functions and data structures for working with maps.
We also include the <iostream> header for input-output operations.
We declare and initialize a map named originalMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the copy constructor to create a new map named copiedMap that contains the same key-value pairs as originalMap.
We print the copied map to the console using a range-based for loop and the std::cout function to verify the copy.

C++ Program

#include <map>
#include <iostream>

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

    // Copy the map using the copy constructor
    std::map<int, std::string> copiedMap(originalMap);

    // Print the copied map
    std::cout << "Copied Map: ";
    for (const auto& pair : copiedMap) {
        std::cout << "{" << pair.first << ", " << pair.second << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Copied Map: {1, one} {2, two} {3, three}

2 Copying a Map Using the Assignment Operator

We can also copy a map in C++ using the assignment operator, which assigns the contents of the original map to a new map.

For example,

We start by including the <map> header file, which provides the necessary functions and data structures for working with maps.
We also include the <iostream> header for input-output operations.
We declare and initialize a map named originalMap with some key-value pairs. In this example, the map has integer keys and string values.
We use the assignment operator to create a new map named copiedMap and assign the contents of originalMap to it.
We print the copied map to the console using a range-based for loop and the std::cout function to verify the copy.

C++ Program

#include <map>
#include <iostream>

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

    // Copy the map using the assignment operator
    std::map<int, std::string> copiedMap = originalMap;

    // Print the copied map
    std::cout << "Copied Map: ";
    for (const auto& pair : copiedMap) {
        std::cout << "{" << pair.first << ", " << pair.second << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Copied Map: {1, one} {2, two} {3, three}

3 Copying a Map Using the insert Method

We can copy a map in C++ by using the insert method to add all key-value pairs from the original map to a new map.

For example,

We start by including the <map> header file, which provides the necessary functions and data structures for working with maps.
We also include the <iostream> header for input-output operations.
We declare and initialize a map named originalMap with some key-value pairs. In this example, the map has integer keys and string values.
We declare an empty map named copiedMap.
We use the insert method to add all key-value pairs from originalMap to copiedMap.
We print the copied map to the console using a range-based for loop and the std::cout function to verify the copy.

C++ Program

#include <map>
#include <iostream>

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

    // Declare an empty map
    std::map<int, std::string> copiedMap;

    // Copy the map using the insert method
    copiedMap.insert(originalMap.begin(), originalMap.end());

    // Print the copied map
    std::cout << "Copied Map: ";
    for (const auto& pair : copiedMap) {
        std::cout << "{" << pair.first << ", " << pair.second << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Copied Map: {1, one} {2, two} {3, three}

Summary

In this tutorial, we learned How to Copy a Map in C++ language with well detailed examples.

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