Artikel
11/18/2011

UTF8Encoding.GetMaxByteCount Method

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Calculates the maximum number of bytes produced by encoding the specified number of characters.

Namespace: System.Text
Assembly: mscorlib (in mscorlib.dll)

Syntax

'Declaration
Public Overrides Function GetMaxByteCount ( _
    charCount As Integer _
) As Integer

public override int GetMaxByteCount(
    int charCount
)

Parameters

charCount
Type: System.Int32
The number of characters to encode.

Return Value

Type: System.Int32
The maximum number of bytes produced by encoding the specified number of characters.

Exceptions

Exception	Condition
ArgumentOutOfRangeException	charCount is less than zero. -or- The resulting number of bytes is greater than the maximum number that can be returned as an integer.

ArgumentOutOfRangeException

charCount is less than zero.

-or-

The resulting number of bytes is greater than the maximum number that can be returned as an integer.

Remarks

To calculate the exact array size required by GetBytes to store the resulting bytes, call the GetByteCount method. To calculate the maximum array size, call the GetMaxByteCount method. The GetByteCount method generally allocates less memory, while the GetMaxByteCount method generally executes faster.

The GetMaxByteCount method returns a worst-case number. If a fallback is chosen with a potentially large string, GetMaxByteCount can return large values.

In most cases, this method returns reasonable numbers for small strings. 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 exceeded. You might also want to consider a different approach using GetByteCount or Encoder.Convert. For example, text in English and many other languages often needs only one UTF-8 byte to represent a character, but the number returned by GetMaxByteCount has to allow for the possibility that the string to be converted will consist entirely of characters that each require four bytes.

GetMaxByteCount has no relation to GetChars. If your application needs a similar function to use with GetChars, it should use GetMaxCharCount.

Note:
GetMaxByteCount(N) is not necessarily the same value as N* GetMaxByteCount(1).

Examples

The following example demonstrates how to use the GetMaxByteCount method to return the maximum number of bytes required to encode a specified number of characters.

Imports System.Text

Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim utf8 As New UTF8Encoding()
      Dim charCount As Integer = 2
      Dim maxByteCount As Integer = utf8.GetMaxByteCount(charCount)
      outputBlock.Text += String.Format( _
          "Maximum of {0} bytes needed to encode {1} characters.", _
          maxByteCount, _
          charCount _
      ) & vbCrLf
   End Sub 
End Class 
' The example displays the following output:
'     Maximum of 9 bytes needed to encode 2 characters.

using System;
using System.Text;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      UTF8Encoding utf8 = new UTF8Encoding();
      int charCount = 2;
      int maxByteCount = utf8.GetMaxByteCount(charCount);
      outputBlock.Text += String.Format(
          "Maximum of {0} bytes needed to encode {1} characters.\n",
          maxByteCount,
          charCount
      );
   }
}
// The example displays the following output:
//     Maximum of 9 bytes needed to encode 2 characters.

Version Information

Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

Platforms

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Freigeben über