C# PREPROCESSOR DIRECTIVES

The preprocessor directives give instruction to the compiler to preprocess the information before actual compilation starts.

All preprocessor directives begin with #, and only white-space characters may appear before a preprocessor directive on a line. Preprocessor directives are not statements, so they do not end with a semicolon (;).

Preprocessor Directives in C#

The #define Preprocessor

The #define preprocessor directive creates symbolic constants.

#define lets you define a symbol such that, by using the symbol as the expression passed to the #if directive, the expression evaluates to true. Its syntax is as follows:

#define PI 
using System;
namespace PreprocessorDAppl
{
    class Program
    {
        static void Main(string[] args)
        {
#if (PI)
            Console.WriteLine("PI is defined");
#else
            Console.WriteLine("PI is not defined");
#endif
            Console.ReadKey();
            //PI is defined
        }
    }
}

Conditional Directives

You can use the #if directive to create a conditional directive. Conditional directives are useful for testing a symbol or symbols to check if they evaluate to true. If they do evaluate to true, the compiler evaluates all the code between the #if and the next directive.

#define DEBUG
#define VC_V10
using System;
public class TestClass
{
    public static void Main()
    {
#if (DEBUG && !VC_V10)
        Console.WriteLine("DEBUG is defined");
#elif (!DEBUG && VC_V10)
        Console.WriteLine("VC_V10 is defined");
#elif (DEBUG && VC_V10)
        Console.WriteLine("DEBUG and VC_V10 are defined");
#else
        Console.WriteLine("DEBUG and VC_V10 are not defined");
#endif
        Console.ReadKey();
        //DEBUG and VC_V10 are defined
    }
}