Getting the value of a multimap in C++

Article by: Manish Methani

Last Updated: September 9, 2021 at 8:04am IST
6 min 53 sec

Table of Contents:

A MultiMap is a versatile data structure in C++ that allows you to store and manage key-value pairs where a key can have multiple associated values. Accessing and retrieving the values associated with a specific key in a MultiMap is a common operation. In this step-by-step guide, we'll walk you through how to get the values of a MultiMap in C++ with code examples.

Step 1: Include the Necessary Headers

First, you need to include the necessary C++ Standard Library headers to work with MultiMaps. You'll need #include <iostream>, which is standard for input and output, and #include <map>, which is used for MultiMap functionality.

#include <iostream>
#include <map>

Step 2: Create a MultiMap

Next, you need to create a MultiMap. You can define a MultiMap with a specific key and associated values. Here's an example:

std::multimap<std::string, int> myMultiMap;

In this example, we've created a MultiMap where the key is a string and the associated values are integers.

Step 3: Insert Key-Value Pairs

Now, let's insert key-value pairs into the MultiMap. You can use the insert method to add entries.

myMultiMap.insert(std::make_pair("apple", 5));
myMultiMap.insert(std::make_pair("banana", 3));
myMultiMap.insert(std::make_pair("apple", 8));
myMultiMap.insert(std::make_pair("cherry", 10));
myMultiMap.insert(std::make_pair("banana", 2));

Step 4: Get Values Associated with a Key

To retrieve the values associated with a specific key in the MultiMap, you can use the equal_range method. This method returns a pair of iterators representing the range of elements with the specified key. You can then iterate through this range to access the associated values.

std::string keyToSearch = "apple";
auto range = myMultiMap.equal_range(keyToSearch);

for (auto it = range.first; it != range.second; ++it) {
    std::cout << keyToSearch << " has value: " << it->second << std::endl;
}

In this example, we search for the key "apple" and iterate through the range of values associated with it. The output will display the associated values.

Step 5: Full Example Code

Here's the complete example code:

#include <iostream>
#include <map>

int main() {
    std::multimap<std::string, int> myMultiMap;
    
    myMultiMap.insert(std::make_pair("apple", 5));
    myMultiMap.insert(std::make_pair("banana", 3));
    myMultiMap.insert(std::make_pair("apple", 8));
    myMultiMap.insert(std::make_pair("cherry", 10));
    myMultiMap.insert(std::make_pair("banana", 2));

    std::string keyToSearch = "apple";
    auto range = myMultiMap.equal_range(keyToSearch);

    for (auto it = range.first; it != range.second; ++it) {
        std::cout << keyToSearch << " has value: " << it->second << std::endl;
    }

    return 0;
}

Output:

apple has value: 5
apple has value: 8

When you run this code, it will display the values associated with the key "apple" in the MultiMap.

Using a MultiMap in C++ allows you to efficiently manage multiple values associated with a key. You can easily retrieve these values using the equal_range method, as demonstrated in this step-by-step guide.