VB.NET Language in a Nutshell, Second Edition

Data Types

The .NET Common Language Runtime (CLR) includes the Common Type System (CTS), which defines the data types that are supported by the CLR. Thus, each of the languages in the .NET Framework (VB, C#, JScript, and Managed C++) implements a subset of a common set of data types. We say subset because, unfortunately, not all of the CTS types are implemented by VB.NET. For instance, the CTS includes some unsigned integer data types that are not implemented in VB.

As an aside, it is possible to use the VB-unsupported data types in VB by direct use of the corresponding Framework Class Library class. Here is an example illustrating the ability to use the unsigned 16-bit integer data type, whose range of values is 0 to 65,535. Note the use of the ToUInt16 method of the Convert class to actually get an unsigned 16-bit integer:

Dim ui As UInt16
ui = Convert.ToUInt16(65535)
MsgBox(ui.ToString)

Thus, the native VB data types are wrappers for the CTS data types. To illustrate, the VB Integer data type is a wrapper for the Int32 structure that is part of the .NET Framework’s System namespace. One of the members of the Int32 structure is MaxValue, which returns the maximum value allowed for this data type. Thus, even though MaxValue is not officially part of VB.NET (nor is it mentioned in the VB documentation), we can write:

Dim i As Integer
MsgBox(i.Maxvalue)   ' Displays 2147483647

Value and Reference Types

The types defined in the CTS fall into three categories:

• Value types

• Reference types ...