C# Null Array

Use null arrays and empty arrays. Test for a null array before accessing an element.

Null array. An array can be null. An array is by default initialized to null. This must be specified explicitly in local variables. The C# language also initializes array reference elements to null when created with the new keyword.NullNullableNew

First example. This example shows that static arrays (such as int[] fields on a type) are by default initialized to null—even if you do not specify this. The same principle holds true if you are using instance objects on a type.Int Array

Here: The example demonstrates the difference between an empty array of zero elements and a null array reference.

Locals: Local variables in the .NET Framework are stored in a separate part of the metadata. They do not implicitly initialize to null.

Fields: Fields that are of a reference type such as an array type like int[] are implicitly assigned to null.

Finally: The example reports that the default(int[]) expression is equal to null. It writes to the screen with Console.WriteLine.

C# program that uses null array references using System; class Program { static int[] _arrayField1 = new int[0]; // Empty array static int[] _arrayField2; // Null static void Main() { // // Shows an empty array is not a null array. // int[] array1 = new int[0]; Console.WriteLine(array1 == null); // // Shows how to initialize a null array. // int[] array2 = null; Console.WriteLine(array2 == null); // // Static and instance field arrays are automatically null. // Console.WriteLine(_arrayField1 == null); // Empty array Console.WriteLine(_arrayField2 == null); // Null // // Default expression for arrays evaluates to null. // Console.WriteLine(default(int[]) == null); } } Output False True False True True

Default value. Array elements are separate from the array reference variable itself and stored separately in memory. The array elements are initialized to null also if the type is a reference type. Value types are initialized to all zero bits.

Tip: It is never worthwhile to loop through an array you allocate and assign all its elements to null. This occurs implicitly in the CLR.

Array: The program allocates a string array of 3 elements. These elements are initialized to null in the runtime and you can test them against null.

Warning: Using an instance member on one of the elements will result in a NullReferenceException.

C# program that tests default values using System; class Program { static void Main() { // // Value for all reference elements in new array is null. // string[] array = new string[3]; Console.WriteLine(array[0] == null); Console.WriteLine(array[1] == null); Console.WriteLine(array[2] == null); } } Output True True True

In a new value array, each element has its memory location set to all zero bits. A 64-bit integer has 64 zero bits. A 4-bit structure (such as the byte type) has 4 zero bits. These values are represented with the decimal value 0.

Info: The memory is never uninitialized or garbage as you would encounter in C or C++. This helps promote program reliability.

Summary. We tested array references for the null value. Array elements are initialized to null at creation. Static and instance array fields are initialized to null implicitly. We used the default() expression to determine a type's default value.
Dot Net Perls
© 2007-2020 Sam Allen. Every person is special and unique. Send bug reports to