unordered_set cbegin() function in C++ STL

The unordered_set::cbegin() method is a built-in function in C++ STL which is used to return a const_iterator pointing to the first element in the unordered_set container. This iterator can point to either the very the first element or first element of any specified bucket in the unordered_set container.

Note: A const_iterator can only be used to access elements, it cannot modify the elements present in the container.

Syntax:

unordered_set_name.cbegin(n)

Parameter: This function accepts a single parameter n. This is an optional parameter and specifies the bucket number. If this parameter is not passed then the cbegin() method will return a const_iterator pointing to the first element of the container and if this parameter is passed then the begin() method will return a const_iterator pointing to the first element of specific bucket in the unordered_set container.

Return Value: This function returns a const_iterator pointing to the first element in the container or a specified bucket in the container.



Below programs illustrate the unordered_set::cbegin() function:

Program 1:

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// C++ program to illustrate the
// unordered_set::cbegin() function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
  
    unordered_set<int> sampleSet;
  
    // Inserting elements in the std
    sampleSet.insert(5);
    sampleSet.insert(10);
    sampleSet.insert(15);
    sampleSet.insert(20);
    sampleSet.insert(25);
  
    auto itr1 = sampleSet.cbegin();
    auto itr2 = sampleSet.cbegin(4);
  
    cout << "First element in the container is: " << *itr1;
    cout << "\nFirst element in the bucket 4 is: " << *itr2;
  
    return 0;
}
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Output:
First element in the container is: 25
First element in the bucket 4 is: 15

Program 2:

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// C++ program to illustrate the
// unordered_set::cbegin() function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
  
    unordered_set<string> sampleSet;
  
    // Inserting elements
    sampleSet.insert("Welcome");
    sampleSet.insert("To");
    sampleSet.insert("GeeksforGeeks");
    sampleSet.insert("Computer Science Portal");
    sampleSet.insert("For Geeks");
  
    auto itr1 = sampleSet.cbegin();
    auto itr2 = sampleSet.cbegin(0);
  
    cout << "First element in the container is: " << *itr1;
    cout << "\nFirst element in the bucket 0 is: " << *itr2;
  
    return 0;
}
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Output:
First element in the container is: Welcome
First element in the bucket 0 is: GeeksforGeeks

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