Queue.GetEnumerator() Method in C#

The Queue.GetEnumerator() method in C# returns an IEnumerator object that allows you to iterate through the elements of a Queue in FIFO (First In, First Out) order. This method is essential for implementing custom iteration logic or using the Queue in foreach loops.

Syntax

Following is the syntax for the GetEnumerator() method −

public virtual System.Collections.IEnumerator GetEnumerator();

Return Value

The method returns an IEnumerator object that can iterate through the Queue elements from the front to the rear.

Using GetEnumerator() with While Loop

The most common way to use GetEnumerator() is with a while loop using MoveNext() and Current properties −

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Queue queue = new Queue();
      queue.Enqueue(100);
      queue.Enqueue(200);
      queue.Enqueue(300);
      queue.Enqueue(400);
      
      Console.WriteLine("Queue elements:");
      IEnumerator enumerator = queue.GetEnumerator();
      
      while (enumerator.MoveNext()) {
         Console.WriteLine(enumerator.Current);
      }
      
      Console.WriteLine("Queue count: " + queue.Count);
   }
}

The output of the above code is −

Queue elements:
100
200
300
400
Queue count: 4

Using GetEnumerator() with Mixed Data Types

Since Queue is non-generic, it can store different data types. The enumerator handles this seamlessly −

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Queue queue = new Queue();
      queue.Enqueue("First");
      queue.Enqueue(42);
      queue.Enqueue(3.14);
      queue.Enqueue('A');
      
      Console.WriteLine("Mixed data types in Queue:");
      IEnumerator enumerator = queue.GetEnumerator();
      
      while (enumerator.MoveNext()) {
         Console.WriteLine($"Value: {enumerator.Current}, Type: {enumerator.Current.GetType().Name}");
      }
   }
}

The output of the above code is −

Mixed data types in Queue:
Value: First, Type: String
Value: 42, Type: Int32
Value: 3.14, Type: Double
Value: A, Type: Char

GetEnumerator() vs Foreach Loop

While GetEnumerator() provides explicit control, foreach loops use it internally for cleaner syntax −

using System;
using System.Collections;

public class Demo {
   public static void Main() {
      Queue queue = new Queue();
      queue.Enqueue("Apple");
      queue.Enqueue("Banana");
      queue.Enqueue("Cherry");
      
      Console.WriteLine("Using GetEnumerator():");
      IEnumerator enumerator = queue.GetEnumerator();
      while (enumerator.MoveNext()) {
         Console.WriteLine(enumerator.Current);
      }
      
      Console.WriteLine("\nUsing foreach (internally uses GetEnumerator()):");
      foreach (object item in queue) {
         Console.WriteLine(item);
      }
   }
}

The output of the above code is −

Using GetEnumerator():
Apple
Banana
Cherry

Using foreach (internally uses GetEnumerator()):
Apple
Banana
Cherry

Key Points

• The enumerator iterates elements in FIFO order (same as dequeue order).

• The enumerator is a snapshot − modifying the Queue during enumeration throws an exception.

• MoveNext() returns true if there are more elements, false otherwise.

• Current property returns the current element without removing it from the Queue.

Conclusion

The Queue.GetEnumerator() method provides explicit control over iteration through Queue elements in FIFO order. While foreach loops are more convenient for simple iterations, GetEnumerator() is useful when you need custom iteration logic or want to understand how enumeration works internally.