C# | How to copy the entire ArrayList to a one-dimensional Array

Last Updated : 01 Feb, 2019

ArrayList.CopyTo Method is used to copy the entire ArrayList to a compatible one-dimensional Array, starting at the beginning of the target array.

Syntax:

public virtual void CopyTo (Array array);

Here, array is the one-dimensional Array which is the destination of the elements copied from ArrayList. The Array must have zero-based indexing.

Exceptions:

ArgumentNullException: If the array is null.
ArgumentException: If the array is multidimensional OR the number of elements in the source ArrayList is greater than the number of elements that the destination array can contain.
InvalidCastException: If the type of the source ArrayList cannot be cast automatically to the type of the destination array.

Below programs illustrate the use of above-discussed method:

Example 1:

// C# code to illustrate the 
// ArrayList.CopyTo Method 
using System; 
using System.Collections; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // Creating an ArrayList 
        ArrayList myList = new ArrayList(); 
  
        // Adding elements to ArrayList 
        myList.Add("A"); 
        myList.Add("B"); 
        myList.Add("C"); 
        myList.Add("D"); 
        myList.Add("E"); 
        myList.Add("F"); 
        myList.Add("G"); 
        myList.Add("H"); 
  
        // Creates and initializes the 
        // one-dimensional target Array. 
        String[] arr = new String[9]; 
  
        arr[0] = "C"; 
        arr[1] = "C++"; 
        arr[2] = "Java"; 
        arr[3] = "Python"; 
        arr[4] = "C#"; 
        arr[5] = "HTML"; 
        arr[6] = "CSS"; 
        arr[7] = "PHP"; 
        arr[8] = "DBMS"; 
  
        Console.WriteLine("Before CopyTo Method: "); 
  
        Console.WriteLine("\nArrayList Contains: "); 
  
        // printing ArrayList elements 
        foreach(Object obj in myList) 
            Console.WriteLine("{0}", obj); 
  
        Console.WriteLine("\nString Array Contains: "); 
  
        // printing String elements 
        foreach(Object obj1 in arr) 
            Console.WriteLine("{0}", obj1); 
  
        Console.WriteLine("After CopyTo Method: "); 
  
        // using CopyTo Method to copy 
        // the entire source ArrayList 
        // to the target Array starting 
        // at index 0 
        myList.CopyTo(arr); 
  
        Console.WriteLine("\nArrayList Contains: "); 
  
        // printing ArrayList elements 
        foreach(Object obj in myList) 
            Console.WriteLine("{0}", obj); 
  
        Console.WriteLine("\nString Array Contains: "); 
  
        // printing String elements 
        foreach(Object obj1 in arr) 
            Console.WriteLine("{0}", obj1); 
    } 
} 

Output:

Before CopyTo Method: 

ArrayList Contains: 
A
B
C
D
E
F
G
H

String Array Contains: 
C
C++
Java
Python
C#
HTML
CSS
PHP
DBMS

After CopyTo Method: 

ArrayList Contains: 
A
B
C
D
E
F
G
H

String Array Contains: 
A
B
C
D
E
F
G
H
DBMS

Example 2:

// C# code to illustrate the 
// ArrayList.CopyTo Method 
using System; 
using System.Collections; 
  
class GFG { 
  
    // Driver code 
    public static void Main() 
    { 
  
        // Creating an ArrayList 
        ArrayList myList = new ArrayList(); 
  
        // Adding elements to ArrayList 
        myList.Add("HTML"); 
        myList.Add("CSS"); 
        myList.Add("PHP"); 
        myList.Add("DBMS"); 
  
        // Creates and initializes the 
        // one-dimensional target Array. 
        // Here array size is only 2 i.e 
        // it can hold only 3 elements. 
        String[] arr = new String[2]; 
  
        Console.WriteLine("Before CopyTo Method: "); 
  
        Console.WriteLine("\nArrayList Contains: "); 
  
        // printing ArrayList elements 
        foreach(Object obj in myList) 
            Console.WriteLine("{0}", obj); 
  
        Console.WriteLine("\nString Array Contains: "); 
  
        // printing String elements 
        foreach(Object obj1 in arr) 
            Console.WriteLine("{0}", obj1); 
  
        Console.WriteLine("After CopyTo Method: "); 
  
        // using CopyTo Method but It will give 
        // Runtime Error as number of elements 
        // in the source ArrayList is greater 
        // than the number of elements that 
        // the destination array can contain 
        myList.CopyTo(arr); 
  
        Console.WriteLine("\nArrayList Contains: "); 
  
        // printing ArrayList elements 
        foreach(Object obj in myList) 
            Console.WriteLine("{0}", obj); 
  
        Console.WriteLine("\nString Array Contains: "); 
  
        // printing String elements 
        foreach(Object obj1 in arr) 
            Console.WriteLine("{0}", obj1); 
    } 
} 

Runtime Error:

Unhandled Exception:
System.ArgumentException: Destination array was not long enough. Check destIndex and length, and the array’s lower bounds
Parameter name: destinationArray

Reference: