How to Merge Two Maps in C++ - Step by Step Examples

How to Merge Two Maps in C++ ?

Answer

To merge two maps in C++, you can use a combination of insert and for loop to add key-value pairs from one map to another. This provides a straightforward way to combine the contents of two maps.

✐ Examples

1 Merging Two Maps Using insert and for Loop

We can merge two maps in C++ by iterating over the second map and inserting each key-value pair into the first map. The insert method adds the key-value pairs to the first 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 two maps named map1 and map2 with some key-value pairs. In this example, both maps have integer keys and string values.
We use a for loop to iterate over the second map and insert each key-value pair into the first map using the insert method.
We print the merged map to the console using a range-based for loop and the std::cout function to verify the merge.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize two maps
    std::map<int, std::string> map1 = {
        {1, "one"},
        {2, "two"}
    };
    std::map<int, std::string> map2 = {
        {3, "three"},
        {4, "four"}
    };

    // Merge map2 into map1
    for (const auto& pair : map2) {
        map1.insert(pair);
    }

    // Print the merged map
    std::cout << "Merged Map: ";
    for (const auto& pair : map1) {
        std::cout << "{" << pair.first << ", " << pair.second << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Merged Map: {1, one} {2, two} {3, three} {4, four}

2 Merging Two Maps Using insert and Range-Based For Loop

We can also merge two maps in C++ using a range-based for loop to iterate over the second map and insert each key-value pair into the first map. The insert method adds the key-value pairs to the first 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 two maps named map1 and map2 with some key-value pairs. In this example, both maps have integer keys and string values.
We use a range-based for loop to iterate over the second map and insert each key-value pair into the first map using the insert method.
We print the merged map to the console using another range-based for loop and the std::cout function to verify the merge.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize two maps
    std::map<int, std::string> map1 = {
        {1, "one"},
        {2, "two"}
    };
    std::map<int, std::string> map2 = {
        {3, "three"},
        {4, "four"}
    };

    // Merge map2 into map1
    for (const auto& [key, value] : map2) {
        map1.insert({key, value});
    }

    // Print the merged map
    std::cout << "Merged Map: ";
    for (const auto& [key, value] : map1) {
        std::cout << "{" << key << ", " << value << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Merged Map: {1, one} {2, two} {3, three} {4, four}

3 Merging Two Maps with Overlapping Keys Using operator[]

We can merge two maps in C++ and handle overlapping keys by using the operator[] method to update the values in the first map. If a key exists in both maps, the value from the second map will overwrite the value in the first 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 two maps named map1 and map2 with some key-value pairs. In this example, both maps have integer keys and string values, and there is an overlapping key.
We use a range-based for loop to iterate over the second map and use the operator[] method to update the values in the first map.
We print the merged map to the console using another range-based for loop and the std::cout function to verify the merge.

C++ Program

#include <map>
#include <iostream>

int main() {
    // Declare and initialize two maps with overlapping keys
    std::map<int, std::string> map1 = {
        {1, "one"},
        {2, "two"}
    };
    std::map<int, std::string> map2 = {
        {2, "TWO"},
        {3, "three"}
    };

    // Merge map2 into map1, updating values for overlapping keys
    for (const auto& [key, value] : map2) {
        map1[key] = value;
    }

    // Print the merged map
    std::cout << "Merged Map: ";
    for (const auto& [key, value] : map1) {
        std::cout << "{" << key << ", " << value << "} ";
    }
    std::cout << std::endl;

    return 0;
}

Output

Merged Map: {1, one} {2, TWO} {3, three}

Summary

In this tutorial, we learned How to Merge Two Maps in C++ language with well detailed examples.

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How to Merge Two Maps in C++ - Step by Step Examples