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C++ STL Tutorial - Map

Map in C++ STL is an associative container that stores elements in key-value pairs. The key is unique and the value can be accessed using the key. Map is implemented as a balanced tree, which provides O(log n) complexity for inserting, searching and deleting operations.

Syntax

std::map<key_type, value_type> map_name;

Examples:

std::map<int, std::string> student_map; // Key: int, value: string
std::map<std::string, float> score_map; // Key: string, value: float

Example

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> student_map;
    student_map[1111] = "John";
    student_map[2222] = "Alice";
    student_map[3333] = "Bob";

    std::cout << "Map size: " << student_map.size() << std::endl;
    std::cout << "Student with roll no. 2222: " << student_map[2222] << std::endl;

    return 0;
}

Output

Map size: 3
Student with roll no. 2222: Alice

Explanation

In the above example, we have defined a map called "student_map" with integer keys and string values. We have added three key-value pairs to the map using the syntax map_name[key] = value.

We can access the value of a key by using map_name[key]. The size() function returns the number of key-value pairs in the map.

Use

Maps are useful for storing and accessing data in key-value form, where keys and values can be of different types. They are particularly useful when performing lookups, as searches can be done in O(log n) time.

#include <iostream>
#include <map>

int main() {
    std::map<std::string, float> score_map;
    score_map["John"] = 75.5;
    score_map["Alice"] = 80.0;
    score_map["Bob"] = 85.5;

    std::string name;
    std::cout << "Enter a student name: ";
    std::cin >> name;

    if (score_map.find(name) != score_map.end()) {
        std::cout << name << "'s score is " << score_map[name] << std::endl;
    } else {
        std::cout << "No record found for " << name << std::endl;
    }

    return 0;
}

In the above example, we have defined a map called "score_map" with string keys and float values. We have added three key-value pairs to the map using the syntax map_name[key] = value.

We then ask the user to enter a student name, and check if the name exists in the map using the find() function. If the key is found, we print the corresponding value. Otherwise, we print a message saying that no record was found.

Important Points

  • Map is a part of the C++ Standard Template Library (STL).
  • It is an associative container that stores elements in key-value pairs.
  • Key is unique and the value can be accessed using the key.
  • It is implemented as a balanced tree, which provides O(log n) complexity for inserting, searching and deleting operations.
  • Maps are useful for storing and accessing data in key-value form, where keys and values can be of different types.

Summary

In summary, map in C++ STL is an associative container that stores elements in key-value pairs. It provides efficient ways to insert, search and delete elements using the key. Maps are useful for storing and accessing data in key-value form, where keys and values can be of different types, and are particularly useful for performing lookups.

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