Iterators in C++ STL

An iterator is an object that behaves like a pointer to traverse and access elements of a container.

• They allow container traversal without exposing internal structure.
• Support container-independent algorithms like sort(), count(), and find().
• Types include Input, Output, Forward, Bidirectional, and Random Access.
• They are declared as container_type::iterator it; or auto it = container.begin();.

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> v = {10, 20, 30, 40};

    // Using iterator to traverse the vector
    for (vector<int>::iterator it = v.begin(); it != v.end(); ++it)
        cout << *it << " "; 

    return 0;
}

10 20 30 40 

Container Iterator Functions

• STL containers provide member functions that return iterators.
• These iterators usually point to the first and last elements of the container.
• Most STL containers support these functions; exceptions include containers with limited access like stack and queue.
• The functions have consistent names across containers for uniformity.

List of all methods that returns the iterator to the containers:

• begin(): Returns an iterator to the beginning of container.
• end(): Returns an iterator to the theoretical element just after the last element of the container.
• cbegin(): Returns a constant iterator to the beginning of container. A constant iterator cannot modify the value of the element it is pointing to.
• cend(): Returns a constant iterator to the theoretical element just after the last element of the container.
• rbegin(): Returns a reverse iterator to the beginning of container.
• rend(): Returns a reverse iterator to the theoretical element just after the last element of the container.
• crbegin(): Returns a constant reverse iterator to the beginning of container.
• crend(): Returns a constant reverse iterator to the theoretical element just after the last element of the container.

#include <iostream>
#include <vector>
using namespace std;

int main()
{
    vector<int> vec = {10, 20, 30, 40, 50};

    // Normal iterator
    cout << "Forward iteration: ";
    for (auto it = vec.begin(); it != vec.end(); ++it)
    {
        cout << *it << " ";
    }
    cout << endl;

    // Constant iterator
    cout << "Forward (read-only) iteration: ";
    for (auto it =