Standard Template Library – Iterators

              You have a container with elements. How will you access it?? You need a hand to pick it up…

Here, iterator is the thing which access the elements of a container.

Features:

• It traverses the container and hides the internal structure.
• It supports find(),sort() and count() algorithms.
• It access the data as input,output. It can traverse in both forward and bidirectional.
• To access it, use container_type::iterator name.

Let us create a c++ program to illustrate the iterators.

#include <iostream>

#include <vector>

using namespace std;

int main()

{

    vector<int> v1 = {100,120,330,440,550};

    // let us traverse the vector using iterator

    for (vector<int>::iterator i1 = v1.begin(); i1 != v1.end(); ++i1)

        cout << *i1 << " ";

    return 0;

}

Output:

100 120 330 440 550

Methods that return the iterator:

‘begin()’ : this function returns the iterator of beginning point of the container.

‘cbegin()’ : This function returns the constant iterator.

‘rbegin()’ : This function returns the reverse iterator.

‘crbegin()’ : This function returns the reverse constant iterator.

‘end()’ : This function returns the iterator of the last element.

‘cend()’ : This function returns the end of constant iterator.

‘rend()’ : This function returns the end of reverse iterator.

‘crend()’ : This function returns the end of constant reverse iterator.

C++ program to illustrate iterator functions:

#include <iostream>

#include <vector>

using namespace std;

int main()

{

    vector<int> v1 = {110, 200, 330,450, 540, 650};

    // iterator as simple

    cout << "The Forward iteration is: ";

    for (auto i1 = v1.begin(); i1!= v1.end(); ++i1)

    {

        cout << *i1 << " ";

    }

    cout << endl;

    // The Constant iterator is

    cout << "Forward iteration in read only format: ";

    for (auto i1 = v1.cbegin(); i1 != v1.cend(); ++i1)

    {

        cout << *i1 << " ";

    }

    cout << endl;

    // The Reverse iterator is

    cout << "The Reverse iteration is: ";

    for (auto i1 = v1.rbegin(); i1 != v1.rend(); ++i1)

    {

        cout << *i1 << " ";

    }

    cout << endl;

    return 0;

}

Output:

The Forward iteration is: 110 200 330 450 540 650

Forward iteration in read only format: 110 200 330 450 540 650

The Reverse iteration is: 650 540 450 330 200 110

Hope, you understood the concept with programming samples. Keep Coding!!!!