C# | Copying the entire ArrayList to 1D Array starting at the specified index (original) (raw)

Last Updated : 23 Jan, 2019

ArrayList.CopyTo(Array, Int32) Method is used to copy the entire ArrayList to a compatible one-dimensional Array, starting at the specified index of the target array.Syntax:

public virtual void CopyTo (Array array, int arrayIndex);

Parameters:

array: It is the one-dimensional Array that is the destination of the elements copied from ArrayList. The Array must have zero-based indexing.arrayIndex: It is the zero-based index in array at which copying begins.

Exceptions:

• ArgumentNullException: If the array is null.
• ArgumentOutOfRangeException: If the arrayIndex is less than zero.
• 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:

CSharp `

// C# code to illustrate the // ArrayList.CopyTo(Array, Int32) // 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");

    // Creates and initializes the
    // one-dimensional target Array.
    String[] arr = new String[6];

    // adding elements to Array
    arr[0] = "HTML";
    arr[1] = "PHP";
    arr[2] = "Java";
    arr[3] = "Python";
    arr[4] = "C#";
    arr[5] = "OS";

    Console.WriteLine("Before Method: ");

    Console.WriteLine("\nArrayList Contains: ");

    // Displaying the elements in myList
    for (int i = 0; i < myList.Count; i++) {
        Console.WriteLine("myList[{0}] : {1}", i, myList[i]);
    }

    Console.WriteLine("\nArray Contains: ");

    // Displaying the elements in arr
    for (int i = 0; i < arr.Length; i++) {
        Console.WriteLine("arr[{0}] : {1}", i, arr[i]);
    }

    Console.WriteLine("After Method: ");

    // Copying the entire source ArrayList
    // to the target Array starting at
    // index 2.
    myList.CopyTo(arr, 2);

    Console.WriteLine("\nArrayList Contains: ");

    // Displaying the elements in myList
    for (int i = 0; i < myList.Count; i++) {
        Console.WriteLine("myList[{0}] : {1}", i, myList[i]);
    }

    Console.WriteLine("\nArray Contains: ");

    // Displaying the elements in arr
    for (int i = 0; i < arr.Length; i++) {
        Console.WriteLine("arr[{0}] : {1}", i, arr[i]);
    }
}

}

`

Output:

Before Method:

ArrayList Contains: myList[0] : A myList[1] : B myList[2] : C myList[3] : D

Array Contains: arr[0] : HTML arr[1] : PHP arr[2] : Java arr[3] : Python arr[4] : C# arr[5] : OS After Method:

ArrayList Contains: myList[0] : A myList[1] : B myList[2] : C myList[3] : D

Array Contains: arr[0] : HTML arr[1] : PHP arr[2] : A arr[3] : B arr[4] : C arr[5] : D

Example 2:

CSharp `

// C# code to illustrate the // ArrayList.CopyTo(Array, Int32) // 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");

    // 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 Method: ");

    Console.WriteLine("\nArrayList Contains: ");

    // Displaying the elements in myList
    for (int i = 0; i < myList.Count; i++) {
        Console.WriteLine("myList[{0}] : {1}", i, myList[i]);
    }

    Console.WriteLine("\nArray Contains: ");

    // Displaying the elements in arr
    for (int i = 0; i < arr.Length; i++) {
        Console.WriteLine("arr[{0}] : {1}", i, arr[i]);
    }

    Console.WriteLine("After Method: ");

    // using 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, 2);

    Console.WriteLine("\nArrayList Contains: ");

    // Displaying the elements in myList
    for (int i = 0; i < myList.Count; i++) {
        Console.WriteLine("myList[{0}] : {1}", i, myList[i]);
    }

    Console.WriteLine("\nArray Contains: ");

    // Displaying the elements in arr
    for (int i = 0; i < arr.Length; i++) {
        Console.WriteLine("arr[{0}] : {1}", i, arr[i]);
    }
}

}

`

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:

• https://docs.microsoft.com/en-us/dotnet/api/system.collections.arraylist.copyto?view=netframework-4.7.2#System_Collections_ArrayList_CopyTo_System_Array_System_Int32_