Include Code Selectively at Build Time - CSharp Language Basics

CSharp examples for Language Basics:Preprocessor

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Introduction

Use the #if, #elif, #else, and #endif preprocessor directives to identify blocks of code.

Use the System.Diagnostics.ConditionalAttribute attribute to define methods that should be called conditionally only.

Control the inclusion of the conditional code using the #define and #undef directives in your code.

Logical Operators Supported by the #if..#endif Directive

Operator Example Description
== #if myFlag == true Equality. Evaluates to true if the symbol myFlag is defined. Equivalent to #if myFlag.
!=#if myFlag != true Inequality. Evaluates to true if the symbol myFlag is not defined. Equivalent to #if !myFlag.
&& #if myFlag && releaseLogical AND. Evaluates to true only if the symbols myFlag and release are defined.
|| #if myFlag || release Logical OR. Evaluates to true if either of the symbols myFlag or release are defined.
()#if (myFlag || win7) && release Parentheses allow you to group expressions. Evaluates to true if the symbols myFlag or win7 are defined and the symbol release is defined.

Demo Code

#define win7/*from w  w w . ja va  2s  . c o  m*/
#define release
#undef  myValue
using System;
using System.Diagnostics;
class MainClass
{
   [Conditional("DEBUG")]
   public static void DumpState()
   {
      Console.WriteLine("Dump some state...");
   }
   public static void Main()
   {
      // Declare a string to contain the platform name
      string platformName;
      #if myFlag       // Compiling for Windows XP
      platformName = "Microsoft Windows XP";
      #elif myValue   // Compiling for Windows 2000
      platformName = "Microsoft Windows 2000";
      #elif win7     // Compiling for Windows 7
      platformName = "Microsoft Windows 7";
      #else           // Unknown platform specified
      platformName = "Unknown";
      #endif
      Console.WriteLine(platformName);
      // Call the conditional DumpState method
      DumpState();
   }
}

Result


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