Represents a nonexistent value. This class cannot be inherited.
Assembly: mscorlib (in mscorlib.dll)
The class represents a nonexistent value. In a database, for example, a column in a row of a table might not contain any data whatsoever. That is, the column is considered to not exist at all instead of merely not having a value. A object represents the nonexistent column. Additionally, COM interop uses the class to distinguish between a VT_NULL variant, which indicates a nonexistent value, and a VT_EMPTY variant, which indicates an unspecified value.
The type is a singleton class, which means only one object exists. The DBNull::Value member represents the sole object. DBNull::Value can be used to explicitly assign a nonexistent value to a database field, although most ADO.NET data providers automatically assign values of when a field does not have a valid value. You can determine whether a value retrieved from a database field is a value by passing the value of that field to the DBNull.Value.Equals method. However, some languages and database objects supply methods that make it easier to determine whether the value of a database field is DBNull::Value. These include the Visual Basic IsDBNull function, the Convert::IsDBNull method, the DataTableReader::IsDBNull method, and the IDataRecord::IsDBNull method.
Do not confuse the notion of nullptr in an object-oriented programming language with a object. In an object-oriented programming language, nullptr means the absence of a reference to an object. represents an uninitialized variant or nonexistent database column.
The following example calls the DBNull.Value.Equals method to determine whether a database field in a contacts database has a valid value. If it does, the field value is appended to the string output in a label.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.