How to Use Regular Expressions in Visual Basic

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Unlike Visual Basic.NET, which has access to the excellent regular expression support of the .NET framework, good old Visual Basic 6 does not ship with any regular expression support. However, VB6 does make it very easy to use functionality provided by ActiveX and COM libraries.

One such library is Microsoft's VBScript scripting library, which has decent regular expression capabilities starting with version 5.5. It implements the same regular expression flavor used in JavaScript, as standardized in the ECMA-262 standard for JavaScript. This library is part of Internet Explorer 5.5 and later. It is available on all computers running Windows XP, Vista, or 7, and previous versions of Windows if the user upgraded to IE 5.5 or later. That includes almost every Windows PC that is used to connect to the Internet.

To use this library in your Visual Basic application, select Project|References in the VB IDE's menu. Scroll down the list to find the item "Microsoft VBScript Regular Expressions 5.5". It's immediately below the "Microsoft VBScript Regular Expressions 1.0" item. Make sure to tick the 5.5 version, not the 1.0 version. The 1.0 version is only provided for backward compatibility. Its capabilities are less than satisfactory.

After adding the reference, you can see which classes and class members the library provides. Select View|Object Browser in the menu. In the Object Browser, select the "VBScript_RegExp_55" library in the drop-down list in the upper left corner. For a detailed description, see the VBScript regular expression reference on this website. Anything said about JavaScript's flavor of regular expressions in the tutorial also applies to VBScript's flavor. The only exception is the character escape support for \xFF and \uFFFF in the replacement text. JavaScript supports these in string literals, but Visual Basic does not.

The only difference between VB6 and VBScript is that you'll need to use a Dim statement to declare the objects prior to creating them. Here's a complete code snippet. It's the two code snippets on the VBScript page put together, with three Dim statements added.

'Prepare a regular expression object
Dim myRegExp As RegExp
Dim myMatches As MatchCollection
Dim myMatch As Match
Set myRegExp = New RegExp
myRegExp.IgnoreCase = True
myRegExp.Global = True
myRegExp.Pattern = "regex"
Set myMatches = myRegExp.Execute(subjectString)
For Each myMatch in myMatches
  MsgBox(myMatch.Value)
Next

Get RegexBuddy and easily use the power of regular expressions with VB 6 and VB.NET.

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