C++ cbegin()

The cbegin() method returns a constant iterator that points to the first element of an unordered_set. A constant iterator allows read-only access to elements and prevents modification. Because unordered_set does not maintain any defined order, the element returned by cbegin() depends on its internal hash table structure.

Syntax

unordered_set_name.cbegin(n);

Return value:

Returns a const_iterator (constant iterator) pointing to the first element in the unordered_set.

Or, alternatively:

unordered_set_name.cbegin(n);

Parameters:

• n (size_type): The bucket index. Must be less than bucket_count().

Return value:

A const_local_iterator pointing to the first element in bucket n. If the bucket is empty, the returned iterator equals cend(n).

Example

This example demonstrates obtaining the starting element of an unordered_set using cbegin():

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main() {
  unordered_set<int> unique_numbers = {10, 5, 20, 15};

  auto it = unique_numbers.cbegin();

  cout << "The first element in internal order is: " << *it << "\n";

  ++it;
  if (it != unique_numbers.cend()) {
    cout << "The second element is: " << *it << "\n";
  }

  // *it = 99; // Error: cannot modify through const_iterator

  return 0;
}

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A sample output of this code is:

The first element in the set's internal order is: 20
The second element is: 5

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Note: Attempting to modify the element pointed to by the const_iterator would result in a compilation error.

Codebyte Example

In this example, the code retrieves a constant iterator for a specific bucket in the unordered_set and prints all elements stored in that bucket:

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