Queue.CopyTo() Method in C#

The Queue.CopyTo() method in C# is used to copy the Queue elements to an existing one-dimensional Array, starting at the specified array index. This method is particularly useful when you need to transfer queue elements into an array while preserving the FIFO (First In, First Out) order.

Syntax

Following is the syntax for the Queue.CopyTo() method −

public virtual void CopyTo(Array arr, int index);

Parameters

• arr − The one-dimensional Array that is the destination of the elements copied from Queue. The Array must have zero-based indexing.

• index − The zero-based index in the array at which copying begins.

Return Value

This method does not return a value. It performs an in-place copy operation on the destination array.

Using CopyTo() with Integer Queue

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<int> queue = new Queue<int>();
      queue.Enqueue(100);
      queue.Enqueue(200);
      queue.Enqueue(300);
      
      Console.Write("Count of elements = ");
      Console.WriteLine(queue.Count);
      Console.WriteLine("Queue...");
      foreach(int i in queue) {
         Console.WriteLine(i);
      }
      
      int[] intArr = new int[5];
      intArr[0] = 1;
      intArr[1] = 2;
      intArr[2] = 3;
      intArr[3] = 4;
      
      queue.CopyTo(intArr, 1);
      
      Console.WriteLine("\nQueue (After CopyTo)");
      foreach(int i in queue) {
         Console.WriteLine(i);
      }
      
      Console.WriteLine("\nArray (After CopyTo)");
      foreach(int i in intArr) {
         Console.WriteLine(i);
      }
   }
}

The output of the above code is −

Count of elements = 3
Queue...
100
200
300

Queue (After CopyTo)
100
200
300

Array (After CopyTo)
1
100
200
300
0

Using CopyTo() with String Queue

Example

using System;
using System.Collections.Generic;

public class Demo {
   public static void Main() {
      Queue<string> queue = new Queue<string>();
      queue.Enqueue("Tim");
      queue.Enqueue("Jack");
      queue.Enqueue("Nathan");
      queue.Enqueue("Tom");
      queue.Enqueue("David");
      queue.Enqueue("Mark");
      
      Console.Write("Count of elements = ");
      Console.WriteLine(queue.Count);
      Console.WriteLine("Queue...");
      foreach(string i in queue) {
         Console.WriteLine(i);
      }
      
      string[] strArr = new string[10];
      strArr[0] = "AB";
      strArr[1] = "BC";
      strArr[2] = "DE";
      strArr[3] = "EF";
      
      queue.CopyTo(strArr, 1);
      
      Console.WriteLine("\nQueue (After CopyTo)");
      foreach(string i in queue) {
         Console.WriteLine(i);
      }
      
      Console.WriteLine("\nArray (After CopyTo)");
      foreach(string i in strArr) {
         Console.WriteLine(i);
      }
   }
}

The output of the above code is −

Count of elements = 6
Queue...
Tim
Jack
Nathan
Tom
David
Mark

Queue (After CopyTo)
Tim
Jack
Nathan
Tom
David
Mark

Array (After CopyTo)
AB
Tim
Jack
Nathan
Tom
David
Mark

Key Points

• The CopyTo() method does not modify the original queue − it remains unchanged after the copy operation.

• The destination array must have sufficient space from the specified index to accommodate all queue elements.

• Elements are copied in the same order they would be dequeued (FIFO order).

• If the destination array is too small, an ArgumentException will be thrown.

Conclusion

The Queue.CopyTo() method provides an efficient way to transfer queue elements into an existing array while preserving their FIFO order. The original queue remains unchanged, making it useful for creating snapshots or backups of queue data for further processing.