How to Iterate Over Entries (Key-Value Pairs) in a Map in C++ - Step by Step Examples

How to Iterate Over Entries (Key-Value Pairs) in a Map in C++ ?

Answer

To iterate over entries (key-value pairs) in a map in C++, you can use a range-based for loop or an iterator. This allows you to access each key-value pair in the map.

✐ Examples

1 Iterating Over Entries Using Range-Based For Loop

We can iterate over entries in a map in C++ using a range-based for loop, which provides a convenient syntax for iterating over all 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 a range-based for loop to iterate over the map. We access each key and value using the first and second members of the map's key-value pairs, respectively.
We print each key and value to the console using the std::cout function to verify that we are iterating over all entries.

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"}
    };

    // Iterate over entries using range-based for loop
    for (const auto& pair : myMap) {
        std::cout << "Key: " << pair.first << ", Value: " << pair.second << std::endl;
    }

    return 0;
}

Output

Key: 1, Value: one
Key: 2, Value: two
Key: 3, Value: three

2 Iterating Over Entries Using Iterator

We can iterate over entries in a map in C++ using an iterator, which provides a flexible way to access each key-value pair 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 declare an iterator for the map using the std::map<int, std::string>::iterator type.
We use a for loop to iterate over the map by incrementing the iterator. We access each key and value using the first and second members of the iterator's key-value pairs, respectively.
We print each key and value to the console using the std::cout function to verify that we are iterating over all entries.

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"}
    };

    // Declare an iterator for the map
    std::map<int, std::string>::iterator it;

    // Iterate over entries using iterator
    for (it = myMap.begin(); it != myMap.end(); ++it) {
        std::cout << "Key: " << it->first << ", Value: " << it->second << std::endl;
    }

    return 0;
}

Output

Key: 1, Value: one
Key: 2, Value: two
Key: 3, Value: three

3 Storing and Iterating Over Entries Separately

We can store entries in a separate vector and then iterate over the vector in C++, which provides a way to work with key-value pairs independently of the map.

For example,

We start by including the <map>, <vector>, and <iostream> header files, which provide the necessary functions and data structures for working with maps, vectors, 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 declare a vector named entries to store the key-value pairs from the map.
We use a range-based for loop to iterate over the map, and we store each key-value pair in the entries vector.
We use another range-based for loop to iterate over the entries vector and print each key and value to the console using the std::cout function to verify that we have stored all entries separately.

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 entries
    std::vector<std::pair<int, std::string>> entries;

    // Extract entries from the map
    for (const auto& pair : myMap) {
        entries.push_back(pair);
    }

    // Iterate over the entries vector
    for (const auto& pair : entries) {
        std::cout << "Key: " << pair.first << ", Value: " << pair.second << std::endl;
    }

    return 0;
}

Output

Key: 1, Value: one
Key: 2, Value: two
Key: 3, Value: three

Summary

In this tutorial, we learned How to Iterate Over Entries (Key-Value Pairs) in a Map in C++ language with well detailed examples.

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How to Iterate Over Entries (Key-Value Pairs) in a Map in C++ - Step by Step Examples