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Maps

Introduction to Maps in C++​

Maps in C++ are part of the Standard Template Library (STL). They are associative containers that store elements in a mapped fashion. Each element has a key value and a mapped value. No two mapped values can have the same key values.

Maps are typically implemented as binary search trees.

Declaration of Maps​

A map in C++ is declared as follows:

map <key_type, data_type> map_name;

For example, to create a map named student that maps an integer to a string, you would write:

map <int, string> student;

Accessing Values in a Map​

The mapped values in a map can be accessed directly using their corresponding key values. For instance, to access the value of student with key 1, you would write:

cout << student[1];

Inserting Values into a Map​

There are two ways you can insert values into a map.

  1. By using the insert function.
student.insert(pair <int, string> (1, "John"));

This statement inserts a key-value pair into the map student with key 1 and value John.

  1. By using the [] operator.
student[2] = "Tom";

This statement inserts a key-value pair into the map student with key 2 and value Tom.

Size of a Map​

The size() function can be used to find the number of elements (key-value pairs) in a map.

cout << student.size();

Checking If a Map Is Empty​

The empty() function returns true if the map is empty and false otherwise.

if(student.empty())
    cout << "The map is empty";
else
    cout << "The map is not empty";

Deleting Elements from a Map​

The erase() function can be used to remove elements from a map.

student.erase(1);

This statement removes the element with key 1 from the map student.

Clearing a Map​

The clear() function removes all elements from the map.

student.clear();

Iterating Over a Map​

You can use an iterator to access the key-value pairs in a map. Here's how you can do it:

map <int, string> :: iterator it;
for(it = student.begin(); it != student.end(); it++)
{
    cout << it->first << " " << it->second << endl;
}

In this code, it->first represents the key and it->second represents the value.

Conclusion​

Maps in C++ STL are a powerful and flexible tool that allow you to store and manipulate data in a key-value format. They are particularly useful when you need to quickly access data associated with specific keys. Keep practicing with maps to become more familiar with their functionality and uses.