C# - Convert List to Array

Convert List, array. A List can be converted to an array. The opposite conversion is also possible. In each conversion, the element types remain the same—strings remain strings.

More complex methods can be implemented. A for-loop can copy elements from a List and add them to an array. But this is more work for the programmer.

List to array. Here we convert a string List into a string array of the same number of elements. At the end, the program prints the array's length.

Step 1 We create a List and populate it with some strings. The List here can only hold strings (or null).

List

Step 2 Next we use ToArray on the List. To test it, we pass the string array to the Test() method.

ToArray

Array

using System;
using System.Collections.Generic;

class Program
{
    static void Main()
    {
        // Step 1: create list.
        List<string> list = new List<string>();
        list.Add("one");
        list.Add("two");
        list.Add("three");
        list.Add("four");
        list.Add("five");

        // Step 2: convert to string array.
        string[] array = list.ToArray();
        Test(array);
    }

    static void Test(string[] array)
    {
        Console.WriteLine("Array received: " + array.Length);
    }
}
Array received: 5

Array to List. We can convert an array of any number of elements to a List that has the same type of elements. There are 3 parts to this example.

Part 1 Here we initialize a new string array containing 5 strings. These are specified as string literals.

Part 2 Here we convert the array to a List with the List constructor. This returns a new List of strings.

Part 3 Here the example converts the array to a List with the ToList() instance method.

using System;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main()
    {
        // Part 1: string array.
        string[] array = new string[]
        {
            "one",
            "two",
            "three",
            "four",
            "five"
        };
        // Part 2: use list constructor.
        List<string> list1 = new List<string>(array);
        Test(list1);

        // Part 3: use ToList method.
        List<string> list2 = array.ToList();
        Test(list2);
    }

    static void Test(List<string> list)
    {
        Console.WriteLine("List count: " + list.Count);
    }
}List count: 5
List count: 5

Implicit conversion error. You may get the "Cannot implicitly convert type" error. This error raised by the compiler tells you that the type needs a regular cast or is not compatible.

Note If your code statement tries to assign a List to an array, you will get this error.

using System.Collections.Generic;

class Program
{
    static void Main()
    {
        List<int> items = null;
        int[] result = new int[0];
        // This does not work.
        items = result;
    }
}Error CS0029
Cannot implicitly convert type 'int[]' to 'System.Collections.Generic.List<int>'

Notes, ToList. The ToList method is an extension method from System.Linq. This kind of method is an addition to normal C# method calls.

ToList

Extension

Readability. It is easy to remember that ToList converts a collection to a List, and ToArray does the same for an array. These methods are well-named.

A summary. It is possible to convert arrays to Lists (and lists to arrays) with this code. We cannot just assign one to the other. The List constructor can also be used.