When #if DEBUG runs

Question

I have this code in my C# class.

#if DEBUG         private const string BASE_URL = "http://www.a.com/"; #else         private const string BASE_URL = "http://www.b.com//"; #endif 

What I wanted to ask is when does the

#if DEBUG 

path in the code get executed?

Does it get executed

1. When I run up a debug session in Visual Studio?
2. When I manually run the exe or dll in question from the debug folder?
3. Any other circumstances I forgot to mention?

Answer 1

#if DEBUG It's a preprocessor definition.

It compiles when you define DEBUG constant. And yes, it's default on Debug Build Configuration.

Visual Studio 2010 Project Properties:

If Define DEBUG constant is checked VS will compile:

private const string BASE_URL = "http://www.a.com/"; 

Else (not checked) VS will compile:

private const string BASE_URL = "http://www.b.com//"; 

Answer 2

It's a preprocessor directive. The code in the DEBUG part is compiled when you do a debug build (more specifically when the DEBUG constant is defined). I.e. if you do a debug build BASE_URL will point to www.a.com. Otherwise it will point to www.b.com.