Published: Wednesday, May 30, 2001
Overview of Changes from VB6 to VB.NET
By Bipin Joshi
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This article discusses the important language changes from VB6/VBScript to VB.NET. When creating
ASP.NET pages, you are required to use a .NET-compatible programming language, such as C#, VB.NET, or
JScript.NET. However, there are some significant changes from VB6/VBScript to VB.NET, which this article
addresses. To learn more about ASP.NET in general, be sure to check out the
ASP.NET Article Index!
Also, for more information be sure to check out Microsoft's article:
Preparing Your Visual Basic 6.0
Applications for the Upgrade to Visual Basic.NET.
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Introduction
With release of Microsoft .NET platform, Visual Basic has emerged into a fully objected
oriented language (dubbed VB.NET). With these radical changes, though, the learning curve
between VB6 and VB.NET might be reasonably high even for experienced programmers. In this
article I will try to list language changes to Visual Basic along with sample examples
wherever appropriate. The list presented here may not be complete but it does cover
majority of features. If you are a VB programmer wanting to shift to VB.NET this is a must
read for you.
Note that currently (as of May 30th, 2001), ASP.NET is in Beta 1, which is freely downloadable
from www.ASP.NET. However, some of the changes discussed
in this article are changes that are proposed for the Beta 2 version, which is scheduled to
be released to the public on June 17th. These areas that are new to Beta 2 (and therefore will
not work with the Beta 1 version of ASP.NET) are marked.
Data Type Changes
The .NET platform provides Common Type System to all the supported languages. This means that
all the languages must support the same data types as enforced by common language runtime. This
eliminates data type incompatibilities between various languages. For example on the 32-bit Windows
platform, the integer data type takes 4 bytes in languages like C++ whereas in VB it takes 2 bytes.
Following are the main changes related to data types in VB.NET:
- Under .NET the Integer data type in VB.NET is also 4 bytes in size.
- VB.NET has no currency data type. Instead it provides decimal as a replacement.
- VB.NET introduces a new data type called Char. The char data type takes 2 bytes and can store
Unicode characters.
- VB.NET do not have Variant data type. To achieve a result similar to variant type you can use Object
data type. (Since every thing in .NET - including primitive data types - is an object, a variable of object type
can point to any data type).
- In VB.NET there is no concept of fixed length strings.
- In VB6 we used the
Type keyword to declare our user defined structures. VB.NET introduces
the structure keyword for the same purpose. The rest of the syntax is same. That is:
Structure MyStruct1
...
End Structure
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Declaring Variables
Consider this simple example in VB6:
In this example VB6 will consider x as variant and y as integer, which is somewhat odd
behavior. VB.NET corrects this problem, creating both x and y as integers. Furthermore,
VB.NET allows you to assign initial values to the variables in the declaration statement itself:
Dim str1 as string="hello"
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VB.NET also introduces Read-Only variables. Unlike constants Read-Only variables can be declared without
initialization but once you assign a value to it, it can not be changed.
'no initialization here
Dim readonly x as integer
'in later code
x=100
'now x can't be changed
x=200 '***** error *********
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Arrays
With VB6, you could programmatically define the lower and upper bounds of an array. In VB.NET, however, an
array's lower bound is always zero. Also, when defining an array like so:
Dim aStates(50) as String
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in actuality, 51 elements are being created, with 0 as the lower bound and 50 as the upper bound! (Note that
in Beta 1 of the VB.NET compiler, the above statement would create 50 elements, from bounds 0 through 49.)
In Part 2 we'll continue our examination of VB.NET's new (and breaking)
features!
Read Part 2!
