UTF32Encoding.GetMaxCharCount(Int32) 方法

定义

命名空间:

System.Text

程序集:

System.Text.Encoding.Extensions.dll

Source:

UTF32Encoding.cs

计算对指定数目的字节进行解码时产生的最大字符数。

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

参数

byteCount

Int32

要解码的字节数。

返回

Int32

对指定数目的字节进行解码时所产生的最大字符数。

例外

ArgumentOutOfRangeException

byteCount 小于零。

或

得到的字节数大于可作为整数返回的最大数量。

DecoderFallbackException

发生回退（有关详细信息，请参阅采用 .NET 的字符编码）

－和－

将 DecoderFallback 设置为 DecoderExceptionFallback。

示例

下面的示例将字符串编码为一个字节数组，然后将这些字节解码为一个字符数组。

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

注解

若要计算存储生成的字符所需的 GetChars 确切数组大小，请调用 GetCharCount 方法。 若要计算最大数组大小，请调用 GetMaxCharCount 方法。 方法 GetCharCount 通常分配较少的内存，而 GetMaxCharCount 该方法的执行速度通常更快。

GetMaxCharCount 是一个最差大小写的数字，包括当前所选 DecoderFallback的最差情况。 如果选择了具有可能较大的字符串的回退， GetMaxCharCount 则可以返回较大的值。

在大多数情况下，此方法返回小字符串的合理数字。 对于大型字符串，可能需要选择使用非常大的缓冲区和捕获错误（在极少数情况下超出更合理的缓冲区）。 你可能还希望考虑其他方法并使用 GetCharCount 或 Convert。

GetMaxCharCount 与 没有关系 GetBytes。 如果需要与 一起使用 GetBytes的类似函数，请使用 GetMaxByteCount。

注意

GetMaxCharCount(N)不一定与相同 N* GetMaxCharCount(1) 。

另请参阅

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