.ToArray() changes the dimension of my array

Question

In my C# program I've created an array of string:

var arrayTest = new string[20];

I need to copy in it some string that I retrive from a List containing 10 strings.

arrayTest = listTest.ToArray();

This works but .ToArray() changes the dimension of my array based on the number of element in the list.

I need to maintain the same size (20) and have the 10 strings and the 10 null (or whatever value..)

Is there a way to accomplish this other than loop listTest ?

Answer 1

Assuming that your list is generic, you can just use its List<T>.CopyTo() method:

listTest.CopyTo(arrayTest);

Rather than the other answers which create another array just to copy from it and then throw it away.

Even for non-generic lists, there are Copy methods on most such classes that, again, allow you to copy the data directly into a target array, rather than calling ToArray first.

Answer 2

You should either use Array.Copy or List<T>.CopyTo

// You can copy either 'List<T>' or 'Array' by using this
Array.Copy(listTest.ToArray(), arrayTest, listTest.Length);

or the method below inspired by Damien_The_Unbeliever

// You can copy 'List<T>' by using this, but it doesn't require a 'ToArray()' function
// It's better to use this if you're copying with 'List<T>'
listTest.CopyTo(arrayTest)

Using the above codes copies the listText's content to arrayTest, and it doesn't modify the rest of the values inside arrayTest.

But should make sure the size of arrayTest is longer or same as listTest's length, otherwise it'll throw an exception.

Why your code didn't work

The original code you have:

arrayTest = listTest.ToArray();

This makes the arrayTest points to a whole new reference, so the size 20 doesn't make any sense, since the array with length 20 will be garbage collected afterwards. Changing 20 to different sizes still results the same.