OOP Standard Template Library (STD)

 
STL (Standard Template Library) is a powerful library in C++ that provides:

✅ Ready-made classes and functions for common data structures and algorithms.
✅ Generic programming — works with any data type using templates.

Components of STL

STL has four main components:

Component	Description	Example
1. Containers	Store data	vector, list, set, map
2. Algorithms	Perform operations on data	sort(), find(), count()
3. Iterators	Access elements in containers	begin(), end()
4. Functors	Function objects used with algorithms	greater<int>()

CONTAINERS

Containers are data structures that hold collections of elements.

They are of 3 types:

Type	Examples	Description
Sequence Containers	vector, list, deque	Store data sequentially
Associative Containers	set, map, multiset, multimap	Store data in sorted order with keys
Unordered Containers	unordered_set, unordered_map	Store data using hash tables

Example: Vector (Dynamic Array)

#include <iostream>

#include <vector>

using namespace std;

int main() {

    vector<int> v = {10, 20, 30};

    v.push_back(40);   // Add element

    v.pop_back();      // Remove last element

    cout << "Vector elements: ";

    for (int x : v)

        cout << x << " ";

    cout << "\nSize: " << v.size() << endl;

    return 0;

}

Output:

Vector elements: 10 20 30 

Size: 3

Example 2: Set (Unique Sorted Elements)

#include <iostream>

#include <set>

using namespace std;

int main() {

    set<int> s = {30, 10, 20, 10};

    cout << "Set elements: ";

    for (int x : s)

        cout << x << " "; // automatically sorted and unique

    return 0;

}

Output:

Set elements: 10 20 30