Encoding.GetMaxCharCount(Int32) Encoding.GetMaxCharCount(Int32) Encoding.GetMaxCharCount(Int32) Encoding.GetMaxCharCount(Int32) Method

Definición

Cuando se reemplaza en una clase derivada, calcula el número máximo de caracteres que se generan al descodificar el número de bytes especificado.When overridden in a derived class, calculates the maximum number of characters produced by decoding the specified number of bytes.

public:
 abstract int GetMaxCharCount(int byteCount);
public abstract int GetMaxCharCount (int byteCount);
abstract member GetMaxCharCount : int -> int
Public MustOverride Function GetMaxCharCount (byteCount As Integer) As Integer

Parámetros

byteCount
Int32 Int32 Int32 Int32

Número de bytes que se van a descodificar.The number of bytes to decode.

Devoluciones

Número máximo de caracteres que se generan al descodificar el número de bytes especificado.The maximum number of characters produced by decoding the specified number of bytes.

Excepciones

Se ha producido una acción de reserva (vea Codificación de caracteres de .NET para obtener una explicación completa)A fallback occurred (see Character Encoding in .NET for complete explanation) - y --and- El valor de DecoderFallback está establecido en DecoderExceptionFallback.DecoderFallback is set to DecoderExceptionFallback.

Ejemplos

El ejemplo siguiente codifica una cadena en una matriz de bytes y, a continuación, descodifica los bytes en una matriz de caracteres.The following example encodes a string into an array of bytes, and then decodes the bytes into an array of characters.

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.
   Encoding^ u32LE = Encoding::GetEncoding( "utf-32" );
   Encoding^ u32BE = Encoding::GetEncoding( "utf-32BE" );
   
   // Use a 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 = "za\u0306\u01FD\u03B2";
   
   // Encode the string using the big-endian byte order.
   array<Byte>^barrBE = gcnew array<Byte>(u32BE->GetByteCount( myStr ));
   u32BE->GetBytes( myStr, 0, myStr->Length, barrBE, 0 );
   
   // Encode the string using 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 );
}

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 = enc->GetChars( bytes );
   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 : 5   12  :za??�
LE array with LE encoding : System.Text.UTF32Encoding : 5   12  :za??�

*/
using System;
using System.Text;

public class SamplesEncoding  {

   public static void Main()  {

      // Create two instances of UTF32Encoding: one with little-endian byte order and one with big-endian byte order.
      Encoding u32LE = Encoding.GetEncoding( "utf-32" );
      Encoding u32BE = Encoding.GetEncoding( "utf-32BE" );

      // Use a 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 = "za\u0306\u01FD\u03B2";

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

      // Encode the string using 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 );

   }


   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 = enc.GetChars( bytes );
      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 : 5   12  :za??�
LE array with LE encoding : System.Text.UTF32Encoding : 5   12  :za??�

*/

Imports System
Imports System.Text
Imports Microsoft.VisualBasic

Public Class SamplesEncoding   

   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 Encoding = Encoding.GetEncoding("utf-32")
      Dim u32BE As Encoding = Encoding.GetEncoding("utf-32BE")

      ' Use a 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)
      Dim myStr As String = "za" & ChrW(&H0306) & ChrW(&H01FD) & ChrW(&H03B2) 

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

      ' Encode the string using the little-endian byte order.
      ' NOTE: In VB.NET, arrays contain one extra element by default.
      '       The following line creates the 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)

   End Sub 'Main


   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 As Char() = enc.GetChars(bytes)
      Console.WriteLine(chars)

   End Sub 'PrintCountsAndChars 

End Class 'SamplesEncoding


'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 : 5   12  :za??�
'LE array with LE encoding : System.Text.UTF32Encoding : 5   12  :za??�

Comentarios

Para calcular el tamaño exacto de matriz requerido GetChars para almacenar los caracteres resultantes, debe usar el GetCharCount método.To calculate the exact array size required by GetChars to store the resulting characters, you should use the GetCharCount method. Para calcular el tamaño máximo de la matriz, use el GetMaxCharCount método.To calculate the maximum array size, use the GetMaxCharCount method. El GetCharCount método generalmente permite asignar menos memoria, mientras que el GetMaxCharCount método generalmente se ejecuta con mayor rapidez.The GetCharCount method generally allows allocation of less memory, while the GetMaxCharCount method generally executes faster.

GetMaxCharCount Recupera un número de caso peor, incluyendo el peor de los casos para el que se han seleccionado actualmente DecoderFallback.GetMaxCharCount retrieves a worst-case number, including the worst case for the currently selected DecoderFallback. Si se elige una acción de reserva con una cadena potencialmente grande, GetMaxCharCount recupera valores grandes.If a fallback is chosen with a potentially large string, GetMaxCharCount retrieves large values.

En la mayoría de los casos, este método recupera un número razonable de las cadenas pequeñas.In most cases, this method retrieves reasonable numbers for small strings. Cadenas de gran tamaño, tendrá que elegir entre usar búferes muy grandes y detectar errores en el caso excepcional de que un búfer más razonable es demasiado pequeño.For large strings, you might have to choose between using very large buffers and catching errors in the rare case that a more reasonable buffer is too small. También puede tener en cuenta un enfoque diferente utilizando GetCharCount o Decoder.Convert.You might also want to consider a different approach using GetCharCount or Decoder.Convert.

GetMaxCharCount no tiene ninguna relación con GetBytes.GetMaxCharCount has no relation to GetBytes. Si necesita una función similar a usar con GetBytes, debe usar GetMaxByteCount.If you needs a similar function to use with GetBytes, you should use GetMaxByteCount.

Cuando se usa GetMaxCharCount, debe asignar el búfer de salida en función del tamaño máximo del búfer de entrada.When using GetMaxCharCount, you should allocate the output buffer based on the maximum size of the input buffer. Si el búfer de salida está restringido en tamaño, puede usar el Decoder.Convert método.If the output buffer is constrained in size, you might use the Decoder.Convert method.

Tenga en cuenta que GetMaxCharCount considera el peor caso para los bytes de una operación del codificador anterior.Note that GetMaxCharCount considers the worst case for leftover bytes from a previous encoder operation. Para la mayoría de las páginas de código, pasando un valor de 0 a este método recupera valores mayores o iguales que 1.For most code pages, passing a value of 0 to this method retrieves values greater than or equal to 1.

Nota

GetMaxCharCount(N) no es necesariamente el mismo valor que N* GetMaxCharCount(1).GetMaxCharCount(N) is not necessarily the same value as N* GetMaxCharCount(1).

Notas a los desarrolladores de herederos

Todos los Encoding implementaciones deben garantizar que ninguna excepción de desbordamiento de búfer se producirá si los búferes según los resultados de cálculos de este método.All Encoding implementations must guarantee that no buffer overflow exceptions occur if buffers are sized according to the results of this method's calculations.

Se aplica a

Consulte también: