How to Traverse a Set with const_iterator in C++?

In this article, we will discuss how to traverse a set with const_iterator in C++. Before going to its implementation, we must know about the set in C++.

What is the Set?

The standard template library (STL) container std::set in C++ displays a sorted collection of different elements. A set's internal comparison object (of type Compare) always indicates a strict weak ordering criterion that the members in the set must always be sorted according to. It indicates that elements are sorted in ascending order by default.

Usually, the std::set function is implemented as a Red-Black Tree or another balanced binary search tree. Logarithmic time complexity is supported by this implementation for the majority of operations, including lookups, insertions, and deletions.

If we attempt to introduce an element that already exists in the set, the insertion process will be unsuccessful since every element in a set must be unique.

For Instance:

Consider the following discrete numbers: {5, 2, 8, 3, 1}. In C++, the parts of std::set are automatically sorted in ascending order. Therefore, the set would have the following internal order: {1, 2, 3, 5, 8}.

The set only contains unique items, so if we try to find a number already in the set, it will not be added again. For example, trying to reload 3 because there are already 3 in the set that will not change the set.

Example:

Let us take an example to illustrate the set in C++.

Output:

What is the Const_iterator in C++?

A sort of iterator called a const_iterator is used in C++ to explore a container (such as std::vector, std::list, or std::set) without permitting the items to be modified by the iterator. It is used to iterate through the elements of a container in a read-only manner.

Example:

Let us take an example to illustrate the const_iterator in C++.

Output:

Traverse a Set with const_iterator:

Constant references to container objects are provided by const_iterator. It means that we cannot change the value but we can just reach it. It helps to deal with unforeseen changes that can occur while touring.

The four functions of the std::set class return constant iterators:

• std::set::cbegin(): This function provides a const iterator that identifies the starting element of the set.
• std::set::cend(): This function returns a const iterator pointing directly after the last element of the set.
• std::set::crbegin(): This function returns a const reverse iterator pointing to the reverse first (or last) element of the set.
• std::set::crend(): This function returns a const reverse iterator that points directly after the first element of the set, which is after the last element.

Pseudocode:

1. First, create a std::set<int> mySet with some elements.
2. After that, obtain a const_iterator at the beginning of mySet.
3. Iterate over the set using the const_iterator:
   1. While the const_iterator is not at the end of the set:
      1. Access the element pointed to by the const_iterator using *.
      2. Perform any desired operations on the element.
      3. Increment the const_iterator to move to the next element in the set.
4. End of traversal.

Example 1:

Output:

Example 2:

Output: