Associative Containers in C++

The C++ Standard Library offers a variety of efficient containers. These containers are simply pattern versions of various storage data structures. Alternative versions, such as template-based implementations of algorithms and iterators in the Standard Library, are also available. However, the containers are only for storing items. The container must have been templated in order to be modular. This enables the container to hold objects of nearly all data type.

Every container has a collection of member functions, and the majority of these share a subset of similar prototypes of these functions. This gives the coder a significant benefit in rapidly figuring out what is provided by the function name and understanding how to utilise them even if the kind of container changes. Only ordered associative containers are considered here.

C++ provides us with a diverse selection of Containers, each with its own set of applications. The Associative Containers are one type of C++ Container. By the end of this session, you should understand why they are termed "Associative" Containers.

In C++, an associative container stores "Sorted Data," as opposed to other Container types. As a result, searching across it and accessing the info is much faster. Yet, it does mean that data entered will take more time (to place it in the correct position).

All container types in C++ are class templates, which implies they can store a wide variety of data types. Additionally, these utilize the same declaration mechanism, making it simple to understand, memorize, and operate with a variety of container types.

Set up the Container

The C++ Set Container is distinguished from other Associative Containers by the fact that it contains "unique and sorted" data. Using unique, we imply that no two data elements in this container are similar. Any redundancies that are input will be eliminated shortly.

A brief code example is provided below to demonstrate the Set Container in operation.

C++ Program:

#include <iostream>
#include <set>
using namespace std;
 
int main(){
    set<int> s01 = {2, 1, 3, 4, 0, 1};
    cout << "OUTPUT: " << s01.size() << endl;
 
    if (!s01.empty()){
        for (int i: s01){
            cout << i << endl;
        }
    }
}

Output:

OUTPUT: 5
0
1
2
3
4

Container with Several Sets

With one exception, the Multi-Set is nearly identical to the Set Container. In contrast to the Set Container, the Multi-set Container permits duplicates of an element to be kept in its container.

Aside from that, the operations that you apply with Set are also compatible with Multi-Set.

Map Container

The Map Container differs from other Associative Containers in that it stores data as key-value pairs. The Key is similar to the value's Identification feature in that it serves to retrieve and obtain values from the Map. Credentials must be distinct, but values may not be.

If you're familiar with Dictionaries in Python, Maps in C++ are very similar.

Here's a few codes with the basic Map Container approach.

C++ Program:

#include <iostream>
#include <map>
using namespace std;
 
int main(){
    map<int, string> m01;
 
    m01.insert(pair<int, string> (1, "Grapes"));
    m01.insert(pair<int, string> (2, "Guava"));
    m01.insert(pair<int, string> (3, "Watermelon"));
 
    map<int, string>::iterator it;
 
    for (it = m01.begin(); it != m01.end(); it++) {
        cout << "Key: " << it->first << "  Value: " << it->second << endl;
    }
 
    return 1;
}

Output:

Key: 1  Value: Grapes
Key: 2  Value: Guava
Key: 3  Value: Watermelon

To insert data into the Map, we apply insert() and pair, just like we did with the Set Container. Insert() enters the data, whereas pair() changes it to the suitable format.

To get to it, we use the iterator and a for loop to go through all of the Key-Value pairs in the map. The first property is used to return the Key, while the second property is used to acquire the Value. So the iterator is a reference, we need to use ->.

Multi-Map Container

A Multi-Map is similar to a map, including one exception. Keys are not required to be distinct; they might be duplicates of one another. The Values of these duplicate Keys, moreover, must be distinct. In brief, either as the Key or the Value must be distinct. A Multi-Map cannot contain two identical Key-Value pairs.

All the others performs similarly to standard maps, with the exception of a minor variation in the declaration.

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