Conditional compilation/execution

Sometimes you need to execute a code based on some settings in the execution environment, debug mode is typical example for this. An example from the real world: when I’m in debug mode I don’t want to check the incoming IP address of the client against my list of allowed IP addresses, but in production environment this is a required feature. How to achieve this?

1. Comment and uncomment the call to CheckIpAddress manually – well, it works but I can bet all my money that you forget to uncomment it before doing deployment to release environment :)
2. Use conditional compilation directives - #if #elif #endif etc., these work against some defined symbol in the assembly, the code block inside #if is compiled or skipped based the symbol in the condition. Skipped means that the code block won’t be in the assembly. This is better solution but the code can become quickly messy, fragmented and hard to read
   
   
   public void TestMethod()

        {
            #if IPCHECK
                CheckIpAddress();         
            #endif         
        }
        
        private void CheckIpAddress()
        {
            // TODO ip check logic
        }


3. Use the Conditional attribute – a method marked with this attribute is called only when the symbol defined in the attribute is present in the calling environment (e.g. assembly). This results in a clearer code than in  the previous case. The method is compiled to assembly, but it is not executed. This is a difference between conditional compilation and conditional attribute 
   
   
   public void TestMethod()

        {
            CheckIpAddress();  
        }
   
        [Conditional("IPCHECK")]
        private void CheckIpAddress()
        {
            // TODO ip check logic
        }

How can you define such a symbol? 

1. Use the #define directive in code - #define IPCHECK
2. In Visual Studio 2010 there is a possibility to set such symbols directly in the UI at the level of project and build configuration   

Project Properties in VS2010

Just a final note, on the picture you can see a checkbox define DEBUG constant, this is checked by default in the Debug configuration, this is why you can by default use the DEBUG symbol in your code (I didn’t recognize this and worked with DEBUG naturally without knowing how it works)

Links:
http://msdn.microsoft.com/en-us/library/aa664622%28v=vs.71%29.aspx
http://www.csharpfriends.com/Articles/getArticle.aspx?articleID=420