Map | Stl Containers | Cplusplus Tutorial

Introduction

The map is a part of the Standard Template Library (STL) in C++. It is an associative container that stores elements in key-value pairs. The keys are unique and act as an identifier to access the corresponding values. The map is implemented as a balanced binary tree, ensuring that key-value pairs are stored in a sorted order based on the keys.

Creating a Map

To create a map in C++, you need to include the <map> header. Here is a simple example:

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    return 0;
}

Inserting Elements

There are several ways to insert elements into a map. You can use the insert method or the subscript operator [].

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    myMap.insert(std::pair<int, std::string>(3, "Three"));
    
    for(const auto &pair : myMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }
    return 0;
}

1: One
2: Two
3: Three

Accessing Elements

You can access elements in a map using the key. If the key does not exist, the map will insert a new element with the default value for the type.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    
    std::cout << "Key 1: " << myMap[1] << std::endl;
    std::cout << "Key 3: " << myMap[3] << std::endl; // This will insert a default value
    
    return 0;
}

Key 1: One
Key 3:

Removing Elements

You can remove elements from a map using the erase method. You can erase elements by key or by iterator.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    myMap[3] = "Three";
    
    myMap.erase(2); // Remove element with key 2
    
    for(const auto &pair : myMap) {
        std::cout << pair.first << ": " << pair.second << std::endl;
    }
    return 0;
}

1: One
3: Three

Finding Elements

You can find elements in a map using the find method. This method returns an iterator to the element if found, or to the end of the map if not found.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    myMap[3] = "Three";
    
    auto it = myMap.find(2);
    if (it != myMap.end()) {
        std::cout << "Found: " << it->first << ": " << it->second << std::endl;
    } else {
        std::cout << "Key not found" << std::endl;
    }
    
    return 0;
}

Found: 2: Two

Map Size

You can get the number of elements in a map using the size method. It returns the number of key-value pairs in the map.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    
    std::cout << "Map size: " << myMap.size() << std::endl;
    
    return 0;
}

Map size: 2

Iterating Over a Map

You can iterate over the elements of a map using iterators. The map provides both constant and non-constant iterators.

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;
    myMap[1] = "One";
    myMap[2] = "Two";
    myMap[3] = "Three";
    
    for(auto it = myMap.begin(); it != myMap.end(); ++it) {
        std::cout << it->first << ": " << it->second << std::endl;
    }
    
    return 0;
}

1: One
2: Two
3: Three

Conclusion

Maps are a powerful and versatile feature of the C++ Standard Template Library. They allow for efficient storage and retrieval of key-value pairs, providing a wide range of operations to manipulate the data. Understanding how to use maps effectively can greatly enhance your ability to manage complex data structures in C++.

Comprehensive Guide to Map in C++