项目
11/18/2011

UTF8Encoding.GetMaxCharCount Method

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

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

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

Syntax

'Declaration
Public Overrides Function GetMaxCharCount ( _
    byteCount As Integer _
) As Integer

public override int GetMaxCharCount(
    int byteCount
)

Parameters

byteCount
Type: System.Int32
The number of bytes to decode.

Return Value

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

Exceptions

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

ArgumentOutOfRangeException

byteCount 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 GetChars to store the resulting characters, call the GetCharCount method. To calculate the maximum array size, call the GetMaxCharCount method. The GetCharCount method generally allocates less memory, while the GetMaxCharCount method generally executes faster.

GetMaxCharCount is a worst-case number. If a fallback is chosen with a potentially large string, GetMaxCharCount 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 GetCharCount or Encoder.Convert.

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

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

Examples

The following example demonstrates how to use the GetMaxCharCount method to return the maximum number of characters produced by decoding a specified number of bytes.

Imports System.Text

Class Example

   Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim utf8 As New UTF8Encoding()
      Dim byteCount As Integer = 8
      Dim maxCharCount As Integer = utf8.GetMaxCharCount(byteCount)
      outputBlock.Text += String.Format( _
          "Maximum of {0} characters needed to decode {1} bytes.", _
          maxCharCount, _
          byteCount _
      ) + vbCrLf
   End Sub 'Main
End Class 'UTF8EncodingExample

using System;
using System.Text;

class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      UTF8Encoding utf8 = new UTF8Encoding();
      int byteCount = 8;
      int maxCharCount = utf8.GetMaxCharCount(byteCount);
      outputBlock.Text += String.Format(
          "Maximum of {0} characters needed to decode {1} bytes.",
          maxCharCount,
          byteCount
      ) + "\n";
   }
}

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.

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