What is const_iterator in C++ STL Containers?

In C++ STL, a const_iterator is also an iterator and is used similarly to a regular iterator but its main purpose is to iterate over the elements of the container without actually modifying them in any way. It is similar to passing constant pointers to a function.

In this article, we will learn what are constant iterators, how to use them in the STL containers, and how they are different from regular iterators.

How to Use const_iterator?

Every container in C++ provides two member functions: cbegin() and cend() that returns the constant iterator to the beginning and end of the container, respectively. We can use these constant iterators to traverse the container. But we keep in mind that they only allow users to read the value not modify it.

Also, if we have a constant container, then we can only use the constant iterator to traverse it.

C++ Program to Iterate Using const_iterator

The below example demonstrates the use of const_iterator to iterate over an STL container vector.

C++

// C++ program to use of const_iterator to iterate over a
// STL container.

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

int main()
{
    // creating STL container: vector
    vector<int> myVector = { 10, 20, 30, 40, 50 };

    // Using const_iterator to iterate over the vector and
    // print it's value
    for (vector<int>::const_iterator it = myVector.cbegin();
         it != myVector.cend(); ++it) {
        cout << *it << " ";
    }

    return 0;
}

Output

10 20 30 40 50 

Explanation: In the above example cbegin() is used to point at the beginning of the vector and cend() points one past the end of the vector and loop iterates over the vector using the printsr and prints the vector elements.