VB Migration Partner


Previous | Index | Next 

[PRB] PreProcess or PostProcess pragma can make VB Migration Partner to hung

A known problem with regular expressions engine is that some special patterns can “freeze” the running program. In reality, no regex pattern can actually crash a .NET application, but there is a category of search patterns that can take such a long time to complete – several minutes even when applied to short strings – that the running program appears to hung. In such cases, the only remedy is to kill the application from Windows Task Manager.

A typical regex pattern that can take long to complete is one that contains nested quantifiers, such as this one


When working with VB Migration Partner, you can bump into this problem when you use the PreProcess and PostProcess pragmas. These pragmas can add a lot of flexibility, but you should be careful in how you use them. If you notice that VB Migration Partner hungs on a specific source code file either during the parse stage or the code generation stage, temporarily remove any PreProcess pragma (in the former case) or PostProcess pragma (in the latter case) and try again. If the problem goes away, it’s time to carefully revise the regex patterns used by your pragmas.

Please read this article for a quick way to temporarily disable all PreProcess and PostProcess pragmas.

Previous | Index | Next 

Follow Francesco Balena on VB6 migration’s group on


Read Microsoft Corp’s official case study of a VB6 conversion using VB Migration Partner.

Code Architects and its partners offers remote and onsite migration services.

More details

Subscribe to our free newsletter for useful VB6 migration tips and techniques.


To learn more about your VB6 applications, run VB6 Analyzer on your source code and send us the generated text file. You will receive a detailed report about your VB6 applications and how VB Migration Partner can help you to quickly and effectively migrate it to .NET.

Get free advice

A fully-working, time-limited Trial Edition of VB Migration Partner allows you to test it against your actual code

Get the Trial

The price of VB Migration Partner depends on the size of the VB6 application, the type of license, and other factors

Request a quote

Migrating a VB6 application in 10 easy steps

Comparing VB Migration Partner with Upgrade Wizard

Migration tools: Feature Comparison Table

All whitepapers