C # Tutorial C # Preprocessor directives

C # Preprocessor Directives

Preprocessor directives instruct the compiler to preprocess information before the actual compilation begins.

All preprocessor directives start with #. And on a single line, only whitespace characters can appear before preprocessor directives. Preprocessor directives are not statements, so they do not end with semicolons (;).

The C # compiler does not have a separate preprocessor, but the instruction is handled as if it had a separate preprocessor. In C #, preprocessor directives are used to work in conditional compilation. Unlike C and C + + directives, they are not used to create macros. A preprocessor directive must be the only instruction on that line.

C # Preprocessor Directives list

The following table lists the preprocessor directives available in C #:

Preprocessor directives

Describe

#define It is used to define a series of characters that become symbols.

#undef It is used to cancel the definition of a symbol.

#if It is used to test whether a symbol is true.

#else It is used to create compound conditional directives for use with #if.

#elif It is used to create compound conditional directives.

#endif Specifies the end of a conditional directive.

#line it allows you to modify the number of lines of the compiler and (optionally) output errors and warning file names.

#error it allows an error to be generated from the specified location in the code.

#warning it allows you to generate a one-level warning from a specified location in your code.

#region It allows you to specify an expandable or collapsed block of code when you use the outline attributes of Visual Studio code Editor.

#endregion it identifies the end of the #region block.

#define Preprocessor

Create symbolic constants #define preprocessor directives.

#define allows you to define a symbol so that the expression returns true by using the symbol as the expression passed to the #if instruction. Its syntax is as follows:

#define Symbol

The following procedure illustrates this:

#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 ();}}}   

When the above code is compiled and executed, it produces the following results:

PI is defined

Conditional directives

You can use #if directives to create a conditional directive. Conditional directives are used to test whether a symbol is true. If true, the compiler executes the code between the #if and the next instruction.

Syntax for conditional directives:

#if symbol [operator symbol] ...

Where symbol is the symbolic name to be tested. You can also use True and false, or put a negative operator before the symbol.

The operator symbol is an operator used to evaluate symbols. The can operator can be one of the following operators:

= = (Equality)

! = (inequality)

&& (and)

|| (OR)

You can also use parentheses to group symbols and operators. Conditional directives are used to compile code when a debug version or a specified configuration is compiled. A conditional instruction that begins with a #if instruction must be signaled to terminate with a #endif instruction.

The following program demonstrates the use of conditional directives:

#define Debug#define vc_v10using 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 is not defined");      #endif      Console.readkey ();   }}

When the above code is compiled and executed, it produces the following results:

DEBUG and VC_V10 are defined

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