C# string[] arrayA return null value in arrayA[3]

Question

I have many array in my code, example;

string[] arrayA = new string[31];

and i need to put the value from the arrays into SQL Database

SqlCommand commA = new SqlCommand("INSERT INTO dbo.DatabaseA" +
            " (ColumnA) VALUES" +
            " (@ColumnA)", connA);
commA.Parameters.Add("@ColumnA", SqlDbType.NVarChar).Value = arrayA[3];

Why does the @ColumnA return error 'the value is not supplied' or to be precise arrayA[3] = null? I always thought unassigned string[] have "" as initial value.

If initially i assigned arrayA[3] = "" before the SQLCommand the code work just fine.

Is there a way to populate the all string[] arrayAwith "" without using for loop?

Possible duplicate of [How to populate/instantiate a C# array with a single value?](http://stackoverflow.com/questions/1014005/how-to-populate-instantiate-a-c-sharp-array-with-a-single-value) — sstan, Aug 11 '16 at 02:27
Declare your array differently. string[] arrayA = Enumerable.Range(0, 31) .Select(i => string.Empty) .ToArray(); — Hakunamatata, Aug 11 '16 at 02:30
The initial value of every item in the array will always be the default value for the array item type. In the case of reference types, including strings, this will always be null. And don't be scared to use loops where needed, they don't bite. — sstan, Aug 11 '16 at 02:30
For your case generating 31 elements using Enumerable will not make any noticeable performance difference. — Hakunamatata, Aug 11 '16 at 06:20

score 4 · Accepted Answer · edited May 23 '17 at 12:14

From the code supplied there is no value assigned to arrayA[3] the array is simply a container for values and sets each value to the default value for the type similar to going default(string).

Now as string is a reference type the default value for the string is null however a value type int for example will have a default value of 0.

We can easily test this such as.

string[] arrayA = new string[31];
var s = arrayA[3]; //is null as string is a reference type

int[] arrayB = new int[31];
var i = arrayB[3]; //equals 0 as default(int) = 0

Now as pointed in comments there are easy ways to populate an array and the referenced comment points to How to populate/instantiate a C# array with a single value?

The snippet below is from the answer above

public static void Populate<T>(this T[] arr, T value ) {
  for ( int i = 0; i < arr.Length;i++ ) {
    arr[i] = value;
  }
}

This can be called by:

arrayA.Populate("");

So in the call:

commA.Parameters.Add("@ColumnA", SqlDbType.NVarChar).Value = arrayA[3];

In fact arrayA[3] = null

EDIT The snippet above is an extension method (as seen by the this keyword on the first parameter in the method signature). This must be in a static class similar to below.

public static class ArrayExtensions
{
    public static void Populate<T>(this T[] arr, T value)
    {
        for (int i = 0; i < arr.Length; i++)
        {
            arr[i] = value;
        }
    }
}

As for the question

Is there a way to populate the all string[] arrayAwith "" without using for loop?

All the methods to set the default value of all items in an array will require a loop of some sort and the loop may be a foreach or for under the hood somewhere.

You could also create a method that would create an array for you of a specified size with a default value.

public static T[] CreateArray<T>(int capacity, T defaultValue)
{
    var array = new T[capacity];
    array.Populate(defaultValue);
    return array;
}

Which could then be called as:

var arrayC = ArrayExtensions.CreateArray<string>(31, "");
s = arrayC[3]; //equals ""

However that starts to look too lazy to me.

The snippit is an extension method (as seen by the `this`) in the first parameter. I will update the answer with an example. — Nico, Aug 11 '16 at 02:41
Thanks for the detailed answer as i I still learning c# and asp.net on my own. — Fahmieyz, Aug 11 '16 at 02:49

score 0 · Answer 2 · answered Aug 11 '16 at 02:51

0

You are not assigned any values to the array . If you need " " ,if there is no value use conditional operators .

arrayA[3]==null?"":arrayA[3];

conditional operators

answered Aug 11 '16 at 02:51

lakshmi prakasan

330
4
12

C# string[] arrayA return null value in arrayA[3]

2 Answers2