UTF32Encoding.GetMaxCharCount(Int32) Metode

Definisi

Ruang nama:

System.Text

Rakitan:

System.Text.Encoding.Extensions.dll

Sumber:

UTF32Encoding.cs

Menghitung jumlah maksimum karakter yang dihasilkan dengan mendekode jumlah byte yang ditentukan.

public:
 override int GetMaxCharCount(int byteCount);

public override int GetMaxCharCount (int byteCount);

override this.GetMaxCharCount : int -> int

Public Overrides Function GetMaxCharCount (byteCount As Integer) As Integer

Parameter

byteCount

Int32

Jumlah byte yang akan didekodekan.

Mengembalikan

Int32

Jumlah maksimum karakter yang dihasilkan dengan mendekode jumlah byte yang ditentukan.

Pengecualian

ArgumentOutOfRangeException

byteCount kurang dari nol.

-atau-

Jumlah byte yang dihasilkan lebih besar dari angka maksimum yang dapat dikembalikan sebagai bilangan bulat.

DecoderFallbackException

Fallback terjadi (untuk informasi selengkapnya, lihat Pengodean Karakter di .NET)

-dan-

DecoderFallback diatur ke DecoderExceptionFallback.

Contoh

Contoh berikut mengodekan string ke dalam array byte, lalu mendekode byte menjadi array karakter.

using namespace System;
using namespace System::Text;
void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc );
int main()
{
   
   // Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
   UTF32Encoding^ u32LE = gcnew UTF32Encoding( false,true,true );
   UTF32Encoding^ u32BE = gcnew UTF32Encoding( true,true,true );
   
   // Create byte arrays from the same string containing the following characters:
   //    Latin Small Letter Z (U+007A)
   //    Latin Small Letter A (U+0061)
   //    Combining Breve (U+0306)
   //    Latin Small Letter AE With Acute (U+01FD)
   //    Greek Small Letter Beta (U+03B2)
   String^ myStr = L"za\u0306\u01FD\u03B2\xD8FF\xDCFF";
   
   // barrBE uses the big-endian byte order.
   array<Byte>^barrBE = gcnew array<Byte>(u32BE->GetByteCount( myStr ));
   u32BE->GetBytes( myStr, 0, myStr->Length, barrBE, 0 );
   
   // barrLE uses the little-endian byte order.
   array<Byte>^barrLE = gcnew array<Byte>(u32LE->GetByteCount( myStr ));
   u32LE->GetBytes( myStr, 0, myStr->Length, barrLE, 0 );
   
   // Get the char counts and decode the byte arrays.
   Console::Write( "BE array with BE encoding : " );
   PrintCountsAndChars( barrBE, u32BE );
   Console::Write( "LE array with LE encoding : " );
   PrintCountsAndChars( barrLE, u32LE );
   
   // Decode the byte arrays using an encoding with a different byte order.
   Console::Write( "BE array with LE encoding : " );
   try
   {
      PrintCountsAndChars( barrBE, u32LE );
   }
   catch ( System::ArgumentException^ e ) 
   {
      Console::WriteLine( e->Message );
   }

   Console::Write( "LE array with BE encoding : " );
   try
   {
      PrintCountsAndChars( barrLE, u32BE );
   }
   catch ( System::ArgumentException^ e ) 
   {
      Console::WriteLine( e->Message );
   }

}

void PrintCountsAndChars( array<Byte>^bytes, Encoding^ enc )
{
   
   // Display the name of the encoding used.
   Console::Write( "{0,-25} :", enc );
   
   // Display the exact character count.
   int iCC = enc->GetCharCount( bytes );
   Console::Write( " {0,-3}", iCC );
   
   // Display the maximum character count.
   int iMCC = enc->GetMaxCharCount( bytes->Length );
   Console::Write( " {0,-3} :", iMCC );
   
   // Decode the bytes and display the characters.
   array<Char>^chars = gcnew array<Char>(iCC);
   enc->GetChars( bytes, 0, bytes->Length, chars, 0 );
   Console::WriteLine( chars );
}

/* 
This code produces the following output.  The question marks take the place of characters that cannot be displayed at the console.

BE array with BE encoding : System.Text.UTF32Encoding : 7   14  :za??�?
LE array with LE encoding : System.Text.UTF32Encoding : 7   14  :za??�?
BE array with LE encoding : System.Text.UTF32Encoding :Invalid byte was found at byte index 3.
LE array with BE encoding : System.Text.UTF32Encoding :Invalid byte was found at byte index 3.

*/

using System;
using System.Text;

public class SamplesUTF32Encoding  {

   public static void Main()  {

      // Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
      UTF32Encoding u32LE = new UTF32Encoding( false, true, true );
      UTF32Encoding u32BE = new UTF32Encoding( true, true, true );

      // Create byte arrays from the same string containing the following characters:
      //    Latin Small Letter Z (U+007A)
      //    Latin Small Letter A (U+0061)
      //    Combining Breve (U+0306)
      //    Latin Small Letter AE With Acute (U+01FD)
      //    Greek Small Letter Beta (U+03B2)
      //    a high-surrogate value (U+D8FF)
      //    a low-surrogate value (U+DCFF)
      String myStr = "za\u0306\u01FD\u03B2\uD8FF\uDCFF";

      // barrBE uses the big-endian byte order.
      byte[] barrBE = new byte[u32BE.GetByteCount( myStr )];
      u32BE.GetBytes( myStr, 0, myStr.Length, barrBE, 0 );

      // barrLE uses the little-endian byte order.
      byte[] barrLE = new byte[u32LE.GetByteCount( myStr )];
      u32LE.GetBytes( myStr, 0, myStr.Length, barrLE, 0 );

      // Get the char counts and decode the byte arrays.
      Console.Write( "BE array with BE encoding : " );
      PrintCountsAndChars( barrBE, u32BE );
      Console.Write( "LE array with LE encoding : " );
      PrintCountsAndChars( barrLE, u32LE );

      // Decode the byte arrays using an encoding with a different byte order.
      Console.Write( "BE array with LE encoding : " );
      try  {
         PrintCountsAndChars( barrBE, u32LE );
      }
      catch ( System.ArgumentException e )  {
         Console.WriteLine( e.Message );
      }

      Console.Write( "LE array with BE encoding : " );
      try  {
         PrintCountsAndChars( barrLE, u32BE );
      }
      catch ( System.ArgumentException e )  {
         Console.WriteLine( e.Message );
      }
   }

   public static void PrintCountsAndChars( byte[] bytes, Encoding enc )  {

      // Display the name of the encoding used.
      Console.Write( "{0,-25} :", enc.ToString() );

      // Display the exact character count.
      int iCC  = enc.GetCharCount( bytes );
      Console.Write( " {0,-3}", iCC );

      // Display the maximum character count.
      int iMCC = enc.GetMaxCharCount( bytes.Length );
      Console.Write( " {0,-3} :", iMCC );

      // Decode the bytes and display the characters.
      char[] chars = new char[iCC];
      enc.GetChars( bytes, 0, bytes.Length, chars, 0 );
      Console.WriteLine( chars );
   }
}

Imports System.Text

Public Class SamplesUTF32Encoding   

   Public Shared Sub Main()

      ' Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
      Dim u32LE As New UTF32Encoding(False, True, True)
      Dim u32BE As New UTF32Encoding(True, True, True)


      ' Create byte arrays from the same string containing the following characters:
      '    Latin Small Letter Z (U+007A)
      '    Latin Small Letter A (U+0061)
      '    Combining Breve (U+0306)
      '    Latin Small Letter AE With Acute (U+01FD)
      '    Greek Small Letter Beta (U+03B2)
      '    a high-surrogate value (U+D8FF)
      '    a low-surrogate value (U+DCFF)
      Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2) & ChrW(&HD8FF) & ChrW(&HDCFF)

      ' barrBE uses the big-endian byte order.
      ' NOTE: In Visual Basic, arrays contain one extra element by default.
      '       The following line creates an array with the exact number of elements required.
      Dim barrBE(u32BE.GetByteCount(myStr) - 1) As Byte
      u32BE.GetBytes(myStr, 0, myStr.Length, barrBE, 0)

      ' barrLE uses the little-endian byte order.
      ' NOTE: In Visual Basic, arrays contain one extra element by default.
      '       The following line creates an array with the exact number of elements required.
      Dim barrLE(u32LE.GetByteCount(myStr) - 1) As Byte
      u32LE.GetBytes(myStr, 0, myStr.Length, barrLE, 0)


      ' Get the char counts and decode the byte arrays.
      Console.Write("BE array with BE encoding : ")
      PrintCountsAndChars(barrBE, u32BE)
      Console.Write("LE array with LE encoding : ")
      PrintCountsAndChars(barrLE, u32LE)


      ' Decode the byte arrays using an encoding with a different byte order.
      Console.Write("BE array with LE encoding : ")
      Try
         PrintCountsAndChars(barrBE, u32LE)
      Catch e As System.ArgumentException
         Console.WriteLine(e.Message)
      End Try

      Console.Write("LE array with BE encoding : ")
      Try
         PrintCountsAndChars(barrLE, u32BE)
      Catch e As System.ArgumentException
         Console.WriteLine(e.Message)
      End Try

   End Sub


   Public Shared Sub PrintCountsAndChars(bytes() As Byte, enc As Encoding)

      ' Display the name of the encoding used.
      Console.Write("{0,-25} :", enc.ToString())

      ' Display the exact character count.
      Dim iCC As Integer = enc.GetCharCount(bytes)
      Console.Write(" {0,-3}", iCC)

      ' Display the maximum character count.
      Dim iMCC As Integer = enc.GetMaxCharCount(bytes.Length)
      Console.Write(" {0,-3} :", iMCC)

      ' Decode the bytes and display the characters.
      Dim chars(iCC) As Char
      enc.GetChars(bytes, 0, bytes.Length, chars, 0)
      Console.WriteLine(chars)

   End Sub

End Class

Keterangan

Untuk menghitung ukuran array yang tepat yang diperlukan oleh GetChars untuk menyimpan karakter yang dihasilkan, Anda memanggil GetCharCount metode . Untuk menghitung ukuran array maksimum, Anda memanggil GetMaxCharCount metode . Metode ini GetCharCount umumnya mengalokasikan lebih sedikit memori, sementara GetMaxCharCount metode umumnya dijalankan lebih cepat.

GetMaxCharCount adalah angka terburuk, termasuk kasus terburuk untuk yang saat ini dipilih DecoderFallback. Jika fallback dipilih dengan string yang berpotensi besar, GetMaxCharCount dapat mengembalikan nilai besar.

Dalam kebanyakan kasus, metode ini mengembalikan angka yang wajar untuk string kecil. Untuk string besar, Anda mungkin harus memilih antara menggunakan buffer yang sangat besar dan menangkap kesalahan dalam kasus yang jarang terjadi bahwa buffer yang lebih masuk akal terlampaui. Anda mungkin juga ingin mempertimbangkan pendekatan dan penggunaan GetCharCount yang berbeda atau Convert.

GetMaxCharCount tidak memiliki hubungan dengan GetBytes. Jika Anda memerlukan fungsi serupa untuk digunakan dengan GetBytes, gunakan GetMaxByteCount.

Catatan

GetMaxCharCount(N) belum tentu nilai yang sama dengan N* GetMaxCharCount(1).

Lihat juga

• GetChars(Byte[], Int32, Int32, Char[], Int32)
• GetString(Byte[], Int32, Int32)
• GetCharCount(Byte[], Int32, Int32)
• GetDecoder()