Arahan C #Proses pemproses

Dalam tutorial ini, kita akan belajar mengenai Arahan Pra-prosesor, arahan yang tersedia di C #, dan kapan, mengapa dan bagaimana mengapa ia digunakan.

Seperti namanya, arahan preprocessor adalah sekatan penyataan yang akan diproses sebelum penyusunan sebenar bermula. Arahan C # preprocessor adalah arahan untuk penyusun yang mempengaruhi proses penyusunan.

Perintah ini menentukan bahagian mana dari kod yang akan dikompilasi atau bagaimana menangani kesalahan dan peringatan tertentu.

Arahan preprocessor C # bermula dengan # (hash)simbol dan semua arahan preprocessor berlangsung selama satu baris. Arahan pemproses dihentikan oleh new linedan bukannya semicolon.

Arahan preprocessor yang terdapat di C # adalah:

Arahan pemproses dalam C #
Arahan Pra-Pemproses Penerangan Sintaks
#if Memeriksa sama ada ungkapan preprocessor benar atau tidak 
 #jika kod ekspresi preprocessor untuk menyusun #endif
#elif Digunakan bersama #ifuntuk memeriksa pelbagai ungkapan praprosesor 
 #if preprocessor-express-code untuk menyusun #elif preprocessor-express-2 code untuk menyusun #endif
#else Digunakan bersama #ifuntuk membuat arahan kompaun bersyarat. 
 #if kod preprocessor-express untuk menyusun kod #elif untuk menyusun #endif
#endif Digunakan bersama #ifuntuk menunjukkan akhir arahan bersyarat 
 #jika kod ekspresi preprocessor untuk menyusun #endif
#define Digunakan untuk menentukan simbol 
 #tentukan SIMBOL
#undef Digunakan untuk menentukan simbol 
 #undef SIMBOL
#warning Membolehkan kami menghasilkan amaran tahap 1 dari kod kami 
 # peringatan-pesanan amaran
#error Membolehkan kami menghasilkan ralat dari kod kami 
 # ralat-ralat-mesej
#line Membolehkan kita mengubah nombor baris dan nama fail penyusun untuk memaparkan kesalahan dan amaran 
 #line-nombor fail-nama fail
#region Membolehkan kita membuat wilayah yang dapat dikembangkan atau runtuh ketika menggunakan Visual Studio Code Editor 
 #kod rujukan wilayah-wilayah #endregion
#endregion Menunjukkan akhir wilayah 
 #kod rujukan wilayah-wilayah #endregion
#pragma Memberi arahan khas penyusun untuk penyusunan fail di mana ia muncul. 
 #pragma pragma-nama pragma-argumen

#tentukan arahan

  • The #definearahan membolehkan kita untuk menentukan simbol.
  • Simbol yang ditentukan semasa digunakan bersama #ifarahan akan dinilai menjadi benar.
  • Simbol-simbol ini dapat digunakan untuk menentukan keadaan penyusunan.
  • Sintaks: 
     #tentukan SIMBOL
  • Sebagai contoh: 
     #menentukan UJIAN
    Di sini, UJIAN adalah simbol.

#undef arahan

  • The #undefarahan membolehkan kita untuk undefine simbol.
  • Undefined symbols when used along with #if directive will evaluate to false.
  • Syntax: 
     #undef SYMBOL
  • For example: 
     #undef TESTING
    Here, TESTING is a symbol.

#if directive

  • The #if directive are used to test the preprocessor expression.
  • A preprocessor expression may consists of a symbol only or combination of symbols along with operators like && (AND), || (OR), ! (NOT).
  • #if directive is followed by an #endif directive.
  • The codes inside the #if directive is compiled only if the expression tested with #if evaluates to true.
  • Syntax: 
     #if preprocessor-expression code to compile< #endif
  • For example: 
     #if TESTING Console.WriteLine("Currently Testing"); #endif

Example 1: How to use #if directive?

 #define CSHARP using System; namespace Directive ( class ConditionalDirective ( public static void Main(string() args) ( #if (CSHARP) Console.WriteLine("CSHARP is defined"); #endif ) ) )

When we run the program, the output will be:

 CSHARP is defined

In the above program, CSHARP symbol is defined using the #define directive at the beginning of program. Inside the Main() method, #if directive is used to test whether CSHARP is true or not. The block of code inside #if directive is compiled only if CSHARP is defined.

#elif directive

  • The #elif directive is used along with #if directive that lets us create a compound conditional directive.
  • It is used when testing multiple preprocessor expression.
  • The codes inside the #elif directive is compiled only if the expression tested with that #elif evaluates to true.
  • Syntax: 
     #if preprocessor-expression-1 code to compile #elif preprocessor-expression-2 code-to-compile #endif
  • For example: 
     #if TESTING Console.WriteLine("Currently Testing"); #elif TRAINING Console.WriteLine("Currently Training"); #endif

#else directive

  • The #else directive is used along with #if directive.
  • If none of the expression in the preceding #if and #elif (if present) directives are true, the codes inside the #else directive will be compiled.
  • Syntax: 
     #if preprocessor-expression-1 code to compile #elif preprocessor-expression-2 code-to-compile #else code-to-compile #endif
  • For example: 
     #if TESTING Console.WriteLine("Currently Testing"); #elif TRAINING Console.WriteLine("Currently Training"); #else Console.WriteLine("Neither Testing nor Training"); #endif

#endif directive

  • The #endif directive is used along with #if directive to indicate the end of #if directive.
  • Syntax: 
     #if preprocessor-expression-1 code to compile #endif
  • For example: 
     #if TESTING Console.WriteLine("Currently Testing"); #endif

Example 2: How to use conditional directive (if, elif, else, endif) ?

 #define CSHARP #undef PYTHON using System; namespace Directive ( class ConditionalDirective ( static void Main(string() args) ( #if (CSHARP && PYTHON) Console.WriteLine("CSHARP and PYTHON are defined"); #elif (CSHARP && !PYTHON) Console.WriteLine("CSHARP is defined, PYTHON is undefined"); #elif (!CSHARP && PYTHON) Console.WriteLine("PYTHON is defined, CSHARP is undefined"); #else Console.WriteLine("CSHARP and PYTHON are undefined"); #endif ) ) )

When we run the program, the output will be:

 CSHARP is defined, PYTHON is undefined

In this example, we can see the use of #elif and #else directive. These directive are used when there are multiple conditions to be tested. Also, symbols can be combined using logical operators to form a preprocessor expression.

#warning directive

  • The #warning directive allows us to generate a user-defined level one warning from our code.
  • Syntax: 
     #warning warning-message
  • For example: 
     #warning This is a warning message

Example 3: How to use #warning directive?

 using System; namespace Directives ( class WarningDirective ( public static void Main(string() args) ( #if (!CSHARP) #warning CSHARP is undefined #endif Console.WriteLine("#warning directive example"); ) ) )

When we run the program, the output will be:

 Program.cs(10,26): warning CS1030: #warning: 'CSHARP is undefined' (/home/myuser/csharp/directives-project/directives-project.csproj) #warning directive example

After running the above program, we will see the output as above. The text represents a warning message. Here, we are generating a user-defined warning message using the #warning directive.

Note that the statements after the #warning directive are also executed. It means that the #warning directive does not terminate the program but just throws a warning.

#error directive

  • The #error directive allows us to generate a user-defined error from our code.
  • Syntax: 
     #error error-message
  • For example: 
     #error This is an error message

Example 4: How to use #error directive?

 using System; namespace Directive ( class Error ( public static void Main(string() args) ( #if (!CSHARP) #error CSHARP is undefined #endif Console.WriteLine("#error directive example"); ) ) )

When we run the program, the output will be:

 Program.cs(10,24): error CS1029: #error: 'CSHARP is undefined' (/home/myuser/csharp/directives-project/directives-project.csproj) The build failed. Please fix the build errors and run again.

We will see some errors, probably like above. Here we are generating a user-defined error.

Another thing to note here is the program will be terminated and the line #error directive example won't be printed as it was in the #warning directive.

#line directive

  • The #line directive allows us to modify the line number and the filename for errors and warnings.
  • Syntax: 
     #line line-number file-name
  • For example: 
     #line 50 "fakeprogram.cs"

Example 5: How to use #line directive?

 using System; namespace Directive ( class Error ( public static void Main(string() args) ( #line 200 "AnotherProgram.cs" #warning Actual Warning generated by Program.cs on line 10 ) ) )

When we run the program, the output will be:

 AnotherProgram.cs(200,22): warning CS1030: #warning: 'Actual Warning generated by Program.cs on line 10' (/home/myuser/csh arp/directive-project/directive-project.csproj)

We have saved the above example as Program.cs. The warning was actually generated at line 10 by Program.cs. Using the #line directive, we have changed the line number to 200 and the filename to AnotherProgram.cs that generated the error.

#region and #endregion directive

  • The #region directive allows us to create a region that can be expanded or collapsed when using a Visual Studio Code Editor.
  • This directive is simply used to organize the code.
  • The #region block can not overlap with a #if block. However, a #region block can be included within a #if block and a #if block can overlap with a #region block.
  • #endregion directive indicates the end of a #region block.
  • Syntax: 
     #region region-description codes #endregion

Example 6: How to use #region directive?

 using System; namespace Directive ( class Region ( public static void Main(string() args) ( #region Hello Console.WriteLine("Hello"); Console.WriteLine("Hello"); Console.WriteLine("Hello"); Console.WriteLine("Hello"); Console.WriteLine("Hello"); #endregion ) ) )

When we run the program, the output will be:

 Hello Hello Hello Hello Hello

#pragma directive

  • The #pragma directive is used to give the compiler some special instructions for the compilation of the file in which it appears.
  • The instruction may include disabling or enabling some warnings.
  • C# supports two #pragma instructions:
    • #pragma warning: Used for disabling or enabling warnings
    • #pragma checksum: It generates checksums for source files which will be used for debugging.
  • Syntax: 
     #pragma pragma-nama pragma-argumen
  • Sebagai contoh: 
     Amaran #pragma dilumpuhkan

Contoh 7: Bagaimana cara menggunakan arahan #pragma?

 using System; namespace Directive ( class Error ( public static void Main(string() args) ( #pragma warning disable #warning This is a warning 1 #pragma warning restore #warning This is a warning 2 ) ) )

Semasa kita menjalankan program, outputnya adalah:

 Program.cs (12,22): amaran CS1030: #warning: 'Ini adalah amaran 2' (/home/myuser/csharp/directive-project/directive-project.csproj)

Kita dapat melihat bahawa hanya amaran kedua yang ditampilkan di skrin output.

Ini kerana, pada mulanya kami mematikan semua amaran sebelum amaran pertama dan memulihkannya hanya sebelum amaran kedua. Inilah sebab mengapa amaran pertama disembunyikan.

Kami juga boleh mematikan amaran khusus dan bukannya semua amaran.

Untuk mengetahui lebih lanjut mengenai #pragma, lawati #pragma (rujukan C #).

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