C# if/then directives for debug vs release

DEBUG/_DEBUG should be defined in VS already.

Remove the #define DEBUG in your code. Set preprocessors in the build configuration for that specific build.

The reason it prints "Mode=Debug" is because of your #define and then skips the elif.

The right way to check is:

#if DEBUG
    Console.WriteLine("Mode=Debug"); 
#else
    Console.WriteLine("Mode=Release"); 
#endif

Don't check for RELEASE.

By default, Visual Studio defines DEBUG if project is compiled in Debug mode and doesn't define it if it's in Release mode. RELEASE is not defined in Release mode by default. Use something like this:

#if DEBUG
  // debug stuff goes here
#else
  // release stuff goes here
#endif

If you want to do something only in release mode:

#if !DEBUG
  // release...
#endif

Also, it's worth pointing out that you can use [Conditional("DEBUG")] attribute on methods that return void to have them only executed if a certain symbol is defined. The compiler would remove all calls to those methods if the symbol is not defined:

[Conditional("DEBUG")]
void PrintLog() {
    Console.WriteLine("Debug info");
}

void Test() {
    PrintLog();
}

I prefer checking it like this over looking for #define directives:

if (System.Diagnostics.Debugger.IsAttached)
{
   //...
}
else
{
   //...
}

With the caveat that of course you could compile and deploy something in debug mode but still not have the debugger attached.

I'm not a huge fan of the #if stuff, especially if you spread it all around your code base as it will give you problems where Debug builds pass but Release builds fail if you're not careful.

So here's what I have come up with (inspired by #ifdef in C#):

public interface IDebuggingService
{
    bool RunningInDebugMode();
}

public class DebuggingService : IDebuggingService
{
    private bool debugging;

    public bool RunningInDebugMode()
    {
        //#if DEBUG
        //return true;
        //#else
        //return false;
        //#endif
        WellAreWe();
        return debugging;
    }

    [Conditional("DEBUG")]
    private void WellAreWe()
    {
        debugging = true;
    }
}

bool isDebug = false;
Debug.Assert(isDebug = true); // '=', not '=='

The method Debug.Assert has conditional attribute DEBUG. If it is not defined, the call and the assignment isDebug = true are eliminated:

If the symbol is defined, the call is included; otherwise, the call (including evaluation of the parameters of the call) is omitted.

If DEBUG is defined, isDebug is set to true (and passed to Debug.Assert , which does nothing in that case).

If you are trying to use the variable defined for the build type you should remove the two lines ...

#define DEBUG  
#define RELEASE 

... these will cause the #if (DEBUG) to always be true.

Also there isn't a default Conditional compilation symbol for RELEASE. If you want to define one go to the project properties, click on the Build tab and then add RELEASE to the Conditional compilation symbols text box under the General heading.

The other option would be to do this...

#if DEBUG
    Console.WriteLine("Debug");
#else
    Console.WriteLine("Release");
#endif

Be sure to define the DEBUG constant in the Project Build Properties. This will enable the #if DEBUG. I don't see a pre-defined RELEASE constant, so that could imply that anything Not in a DEBUG block is RELEASE mode.

https://i.stack.imgur.com/jD7cV.png

Remove your defines at the top

#if DEBUG
        Console.WriteLine("Mode=Debug"); 
#else
        Console.WriteLine("Mode=Release"); 
#endif

NameSpace

using System.Resources;
using System.Diagnostics;

Method

   private static bool IsDebug()
    {
        object[] customAttributes = Assembly.GetExecutingAssembly().GetCustomAttributes(typeof(DebuggableAttribute), false);
        if ((customAttributes != null) && (customAttributes.Length == 1))
        {
            DebuggableAttribute attribute = customAttributes[0] as DebuggableAttribute;
            return (attribute.IsJITOptimizerDisabled && attribute.IsJITTrackingEnabled);
        }
        return false;
    }

Slightly modified (bastardized?) version of the answer by Tod Thomson as a static function rather than a separate class (I wanted to be able to call it in a WebForm viewbinding from a viewutils class I already had included).

public static bool isDebugging() {
    bool debugging = false;

    WellAreWe(ref debugging);

    return debugging;
}

[Conditional("DEBUG")]
private static void WellAreWe(ref bool debugging)
{
    debugging = true;
}

A tip that may save you a lot of time - don't forget that even if you choose debug under the build configuration (on vs2012/13 menu it's under BUILD => CONFIGURATION MANAGER) - that's not enough.

You need to pay attention to the PUBLISH Configuration, as such:

https://i.stack.imgur.com/AOaGO.png

It is worth noting here that one of the most significant differences between conditionally executing code based on #if DEBUG versus if(System.Diagnostics.Debugger.IsAttached) is that the compiler directive changes the code that is compiled. That is, if you have two different statements in an #if DEBUG/#else/#endif conditional block, only one of them will appear in the compiled code. This is an important distinction because it allows you do do things such as conditionally compile method definitions to be public void mymethod() versus internal void mymethod() depending on build type so that you can, for example, run unit tests on debug builds that will not break access control on production builds, or conditionally compile helper functions in debug builds that will not appear in the final code if they would violate security in some way should they escape into the wild. The IsAttached property, on the other hand, does not affect the compiled code. Both sets of code are in all of the builds - the IsAttached condition will only affect what is executed. This by itself can present a security issue.

I got to thinking about a better way. It dawned on me that #if blocks are effectively comments in other configurations (assuming DEBUG or RELEASE; but true with any symbol)

public class Mytest
    {
        public DateTime DateAndTimeOfTransaction;
    }

    public void ProcessCommand(Mytest Command)
        {
            CheckMyCommandPreconditions(Command);
            // do more stuff with Command...
        }

        [Conditional("DEBUG")]
        private static void CheckMyCommandPreconditions(Mytest Command)
        {
            if (Command.DateAndTimeOfTransaction > DateTime.Now)
                throw new InvalidOperationException("DateTime expected to be in the past");
        }

Remove the definitions and check if the conditional is on debug mode. You do not need to check if the directive is on release mode.

Something like this:

#if DEBUG
     Console.WriteLine("Mode=Debug"); 
#else
    Console.WriteLine("Mode=Release"); 
#endif

Since the purpose of these COMPILER directives are to tell the compiler NOT to include code, debug code,beta code, or perhaps code that is needed by all of your end users, except say those the advertising department, i.e. #Define AdDept you want to be able include or remove them based on your needs. Without having to change your source code if for example a non AdDept merges into the AdDept. Then all that needs to be done is to include the #AdDept directive in the compiler options properties page of an existing version of the program and do a compile and wa la! the merged program's code springs alive!.

You might also want to use a declarative for a new process that is not ready for prime time or that can not be active in the code until it's time to release it.

Anyhow, that's the way I do it.