预处理器指令不可能定义或取消定义预处理器

Question

I'm trying to learn preprocessor directive, so I made a simple example like this:

using System;

namespace learning
{
    class Program
    {
        static void Main(string[] args)
        {
#define DEBUG
            test();
        }

        private void test()
        {
#if DEBUG
            Console.WriteLine("Debug mode");
#elif RELEASE
            Console.WriteLine("Release mode");
#else
            Console.WriteLine("Debug and release don't defined");
#endif
        }

    }
}

but I got unfortunately this error:

Impossible to define or cancel defining the preprocessor symbols after the first token in the file

I take this example from a programming book, what is wrong?

update (my solution):

#define RELEASE
using System;

namespace learning
{
    class Program
    {
        static void Main(string[] args)
        {
#if DEBUG
            Console.WriteLine("Debug mode");
#elif RELEASE
            Console.WriteLine("Release mode");
#else
            Console.WriteLine("Debug and release don't defined");
#endif
            Console.ReadLine();
        }

    }
}

printed result: Debug mode , but should be Release mode . What I did wrong?

Answer 1

As Neo mentioned, you can define it at the top of your file.

Or, if you want for it to be global, and you are using Visual Studio, you could define it in your project properties (right-click on the project, choose Properties, then go to the Build tab).

That screen would allow you to define the symbol based upon the build configuration (so you could set your symbol for debug builds and have it automatically be removed when you switch configurations).

If you are not using Visual Studio, you could pass your conditional symbols to MSBuild or csc (the command line build or command line c# compiler). All of these options would give you the ability to set/unset symbols without changing the source code.

Answer 2

您需要在using语句之前将#define行放在文件的开头