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C# in a Nutshell by Peter Drayton, Ted Neward, Ben Albahari

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Name

DBNull

Synopsis

DBNull indicates the absence of information, typically in a database application in which a field does not contain any data. The types in the System.Data.SqlTypes namespace have built-in support for DBNull.

Note that Value is not the same as the null keyword in C#. The null keyword can be used to release an object by clearing the reference. System.DBNull.Value, on the other hand, is a reference to a special value (a member of the singleton class DBNull) that is used to indicate missing information.

This class has some other uses, namely in COM Interop, in which it represents a VT_EMPTY variant (as opposed to a VT_NULL variant, which is a null reference).

public sealed class DBNull : System.Runtime.Serialization.ISerializable, IConvertible {
// Public Static Fields
   public static readonly field DBNull Value;  
// Public Instance Methods
   public method void GetObjectData(                            // implements ISerializable
        System.Runtime.Serialization.SerializationInfo info, 
        System.Runtime.Serialization.StreamingContext context);  
   public method TypeCode GetTypeCode();                         // implements IConvertible
   public override method string ToString();                     // overrides object
   public method string ToString(IFormatProvider provider);     // implements IConvertible
}

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