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Conditional Compilation in ASP.NET 2.0

Include or Exclude Portions of Code from the Compilation Unit





Conditional Compilation in ASP.NET 2.0

Include or Exclude Portions of Code from the Compilation Unit


By Joydip Kanjilal


Conditional compilation dates back to the good old days of the C language. We could conditionally compile a program written in C, i.e., using a pre-defined constant. ASP.NET 2.0 comes with the conditional compilation feature that enables you to compile a specific portion of your code using some pre-defined conditional compilation directives, while excluding the rest of the code from the compilation unit. This article discusses how you can use this feature, and provides code examples for better understanding.


Conditional compilation is implemented using string constants in our code. These are also known as symbols. We need to define these constants either at the page or at the application level and then use them in our code. This section discusses how we can use this feature of ASP.NET in our applications.


Let s consider that we require a C# method to compile conditionally based on the target platform; i.e., a portion of the method would compile if the target is the Mono Framework, while the other would compile if the target is the Microsoft .NET Framework. The following code snippet illustrates how we can use constants in our code to achieve this:


public void SampleMethod ()


   #if MONO_Framework

   //Code targetted at the MONO Framework


   //Code targetted at the Microsoft.NET Framework



Note that if we want to compile the above method in the Mono platform, we should define this constant. On the other hand, if we want our code to be compiled in the Microsoft .NET Framework, we would not define this constant. Note that if this constant is not defined, the if construct in the method shown above becomes false and, hence, any code within it would not be considered for compilation.


Conditional compilation can be done in two ways; i.e., either at the page level in the Page directive or at the application level in the web.config file to make this constant globally accessible by all the pages of the application.


To define at the page level, use the following snippet:


<%@ Page Language="C#" ... CompilerOptions="/d:MONO" %>


The /d switch as shown in the above code snippet is used to define a symbol. To define the same at the application level, use the following snippet in the web.config file:




   <compiler language="c#;cs;csharp" extension=

    ".cs" compilerOptions="/d:MONO"


     System, Version=, Culture=neutral,

     PublicKeyToken=b77a5c561934e089" />




Conditional compilation is a new feature of ASP.NET. This article has discussed what conditional compilation is and how we can use this feature in ASP.NET 2.0 applications. I hope you find this article useful and I welcome comments and suggestions.


Working extensively in Microsoft technologies for more than 10 years, Joydip Kanjilal is a Senior Technical Leader in the Design and Architecture team for a company in Hyderabad, India. His programming skills include C, C++, Java, C#, VB, VC++, ASP.NET, XML, and UML. An ASP.NET MVP, he has worked with .NET and C# for more than five years. Reach Joydip at mailto:[email protected] or at his blog at:





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