VB.NET Language in a Nutshell, Second Edition

Name

CType Function

Named Arguments

No

Syntax

CType(expression, typename)

expression (required; any)

The data item to be converted

typename (required; Keyword)

The data type, object type, structure, or interface to which expression is to be converted

Return Value

expression cast as a typename interface, object, structure, or data type

Description

Converts an expression to the specified data type if possible; otherwise, returns an error.

Rules at a Glance

• expression can be any data, object, structure, or interface type.

• typename can be any data type (such as Boolean, Byte, Decimal, Long, Short, String, etc.), structure type, object type, or interface that can be used with the As clause in a Dim statement.

• If the function fails, or if the converted value of expression is outside the range allowed by typename, an InvalidCastException exception occurs.

• When Option Strict is set to On, then implicit data type conversions can only be widening; that is, implicit data type conversion only occurs from smaller data types to “wider” data types, such as from Integer to Long. In this case, to perform a narrowing type conversion, we can use CType. For instance, if Option Strict is On, the following code produces an error:

  Dim iInteger As Integer = 1
  Dim lLong As Long = 2
  iInteger = lLong
  On the other hand, the following code is fine:
  Dim iInteger As Integer = 1
  Dim lLong As Long = 2
  iInteger = Ctype(lLong, Integer)

Example

Option Strict On Imports Microsoft.VisualBasic Imports System Interface IEmployee ...