TypeName Function

TypeName Function

Class

Microsoft.VisualBasic.Information

Syntax

 TypeName(   varname   )

varname (required; String literal): Name of a variable

Return Value

String

Description

Returns a string giving data type information about varname . The possible return values are:

String returned	Variable contents
`Boolean`	8-bit `True` or `False` value type
`Byte`	8-bit binary value type
`Char`	16-bit character value type
`Date`	64-bit date and time value type
`DBNull`	Reference type indicating missing or nonexistent data
`Decimal`	96-bit fixed point numeric value type
`Double`	64-bit floating point numeric value type
`Error`	`Error` object
`Integer`	32-bit integer value type
`Long`	64-bit integer value type
`Nothing`	Object variable with no object currently assigned to it, uninitialized string, or undimensioned array
`Object`	Reference type pointing to an unspecialized object
`Short`	16-bit integer value type
`Single`	32-bit floating point numeric value type
`String`	Reference type pointing to a string of 16-bit characters
< `objectclass` >	Reference type pointing to a specialized object created from class `<` `objectclass` `>`
< `structure` >	A variable created from a structure or user -defined type named `structure`
< `typename` >( )	Dimensioned array

Rules at a Glance

If varname is declared as type Object, it returns the data subtype that has been assigned to it.
varname returns the data type name of all value types. It returns Nothing for uninitialized reference types and the data type name for all initialized reference types.
If varname is an array that has been initialized or dimensioned, the returned string will be the entry in the previous table corresponding to the underlying data type of the array, but with empty parentheses appended to the end of the name. For example, if varname points to an array of integers, TypeName returns Integer( ) .
When TypeName returns the name of a reference type, such as a class, it only returns the simple name, not the qualified name. For example, if varname points to an object of class System.Drawing.Printing.PaperSource, TypeName returns PaperSource .
If varname is of type Object, TypeName returns the data subtype stored to that object.

Example

 Dim obj As Object obj = New CEmployee(  ) MsgBox(TypeName(obj))     ' Displays: CEmployee obj = 100 MsgBox(TypeName(obj))     ' Displays: Integer obj = Nothing MsgBox(TypeName(obj))     ' Displays: Nothing

Programming Tips and Gotchas

The TypeName function also works directly with members of the Foundation Class Library that aren't wrapped by Visual Basic. It reports the following data types:

String returned	Variable contents
UINT16	Unsigned 16-bit integer
UINT32	Unsigned 32-bit integer
UINT64	Unsigned 64-bit integer
SBYTE	Signed byte

VB.NET/VB 6 Differences

In VB 6, the call to the TypeName function in the code fragment:
```
 Dim strVar As String Console.WriteLine(TypeName(strVar)) 
```
returns a String. In VB.NET, the TypeName function in an equivalent code fragment returns Nothing . This is because in VB.NET, strings are reference types and reference types are implemented as objects.
In VB 6, passing a user-defined type to the TypeName function generates a compile error. In VB.NET, it returns the name of the user-defined type or structure.
In VB 6, passing an uninitialized array to the TypeName function returns the type name plus parentheses. In VB.NET, it returns Nothing .
In VB 6, a variable whose type is not declared is reported as a Variant; in VB . NET, it is an object.