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C# #if Directive

Syntax

#if expression
   // code to include if the expression is true
#endif

Example

#define DEBUG

using System;

class TestClass 
{
    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
    }
}

Output

DEBUG is defined

Explanation

The #if directive is a preprocessor directive in C# that conditionalizes source code during compilation. It allows sections of code to be compiled depending on whether an expression is defined or not. If the expression is defined and evaluated to true, the section of code between the #if and #endif directives is included in the compiled binary.

Sometimes it is necessary to define different code based on the platform, the configuration, or the presence of specific symbols. The #if directive makes it possible to conditionally include or exclude sections of code, based on the value of a specified expression.

Use

The #if directive can be useful for a variety of reasons:

  • To create platform-specific code: for example, if certain code is compatible only with a specific platform.

  • To apply different code during development and production: for example, to enable debug logging only during development and disable it in production.

  • To prevent inclusion of certain code in certain scenarios: for example, to include code only for specific versions or builds of software.

  • To provide different functionality depending on the environment: for example, detecting whether a file exists only when running on a local machine.

Important Points

  • The expression must evaluate to a boolean value.

  • If the expression is not defined, the code between the #if and #endif directives is not included in the compiled binary.

  • The #if directive can be used with the #else and #elif directives to define alternative sections of code.

  • The #if directive can be used with the #define directive to define symbols for the specified expression.

Summary

The #if directive in C# is a powerful tool for including or excluding sections of code based on the value of an expression. It is commonly used to create platform-specific code, apply different code during development and production, and prevent inclusion of certain code in certain scenarios. Understanding the syntax and use cases of this directive can help developers write more efficient, flexible, and optimized code for a wide variety of scenarios.

#ifndef#else
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