C++ List::cbegin() Function

The C++ std::list::cbegin() function is used to retrieve a constant iterator to the first element of the list. The cbegin() function is similar to the begin() function in C++ std::list. Where, the begin() function is used to retrieve an iterator to the first element of the list, whereas the cbegin() function returns a constant iterator to the first element of the list.

The difference between the iterator and constant iterator is that the constant iterator can't be used to modify the content that points to.

Syntax

Following is the syntax of the C++ std::list::cbegin() function −

const_iterator cbegin() const;

Parameters

  • It does not accept any parameter.

Return Value

This function returns a constant iterator.

Example 1

In the following program, we are using the C++ std::list::cbegin() function to retrieve a constant iterator to the first ( or beginning) element of the current list {10, 20, 30, 40, 50}.

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

int main() {
   //create a list
   list<int> num_list = {10, 20, 30, 40, 50};
   cout<<"List elements are: ";
   for(int n : num_list) {
      cout<<n<<" ";
   }
   auto ri = num_list.cbegin();
   cout<<"\nThe constant iterator of the first element: ";
   cout<<*ri;
}

Output

Following is the output of the above program −

List elements are: 10 20 30 40 50 
The constant iterator of the first element: 10

Example 2

Apart from the int-type list element, you can also retrieve an iterator of any other type list element like char and string list content.

Following is another example of the C++ std::list::cbegin() function. Here, we are creating a list(type char) named vowels with the values {'a', 'e', 'i', 'o', 'u'}. Then using the cbegin() function, we are trying to retrieve a constant iterator to the first element of the current list.

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

int main() {
   //create a list
   list<char> vowels = {'a', 'e', 'i', 'o', 'u'};
   cout<<"List elements are: ";
   for(char v : vowels) {
      cout<<v<<" ";
   }
   auto ri = vowels.cbegin();
   cout<<"\nThe constant iterator of the first element: ";
   cout<<*ri;
}

Output

This will generate the following output −

List elements are: a e i o u 
The constant iterator of the first element: a

Example 3

If the list type is a string.

In this example, we are creating a list(type string) named fname with the values {"Rohan", "Reema", "Geeta", "Seema"}. Then, using the cbegin() function, we are trying to retrieve a constant iterator to the first element of the current list.

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

int main() {
   //create a list
   list<string> names = {"Rohan", "Reema", "Geeta", "Seema"};
   cout<<"List elements are: ";
   for(string s : names) {
      cout<<s<<" ";
   }
   auto ri = names.cbegin();
   cout<<"\nThe constant iterator of first element: ";
   cout<<*ri;
}

Output

The above program produces the following output −

List elements are: Rohan Reema Geeta Seema 
The constant iterator of the first element: Rohan

Example 4

Using for loop along with the cbegin() function to retrieve the iterator of the container element.

In this example, we use the cbegin() function along with the for loop to loop through the current container {1, 2, 3, ,4 ,5} and retrieve a constant iterator of all elements in the container starting from the first element.

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

int main() {
   //create a list
   list<int> num_list = {1, 2, 3, 4 ,5};
   cout<<"List elements are: ";
   for(int n : num_list) {
      cout<<n<<" ";
   }
   cout<<"\nA constant iterator of an elements are : ";
   for(auto i = num_list.cbegin(); i!=num_list.end(); i++) {
      cout<<*i<<" ";
   }
}

Output

On executing the above program, it will produce the following output −

List elements are: 1 2 3 4 5 
A constant iterator of an elements are : 1 2 3 4 5
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