Encoding.GetMaxByteCount Method
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When overridden in a derived class, 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 MustOverride Function GetMaxByteCount ( _
charCount As Integer _
) As Integer
public abstract 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. |
| EncoderFallbackException | A fallback occurred (see Understanding Encodings for complete explanation). |
Remarks
The charCount parameter actually specifies the number of Char objects that represent the Unicode characters to encode, because the .NET Framework internally uses UTF-16 to represent Unicode characters. Consequently, most Unicode characters can be represented by one Char object, but a Unicode character represented by a surrogate pair, for example, requires two Char objects.
To calculate the exact array size required by the GetBytes method to store the resulting bytes, the application should use GetByteCount. To calculate the maximum array size, it should use GetMaxByteCount, which returns a worst-case number. The GetByteCount method generally allocates less memory, while the GetMaxByteCount method generally executes faster.
In most cases, this method retrieves reasonable values for small strings. For large strings, you might have to choose between using very large buffers and catching errors in the rare case when a more reasonable buffer is too small. You might also want to consider a different approach using GetByteCount or Encoder.Convert.
When using GetMaxByteCount, your application should allocate the output buffer based on the maximum size of the input buffer. If the output buffer is constrained in size, the application might use the Convert method.
.gif "Note") Note: |
|---|
GetMaxByteCount(N) is not necessarily the same value as N* GetMaxByteCount(1). |
Notes to Implementers
All Encoding implementations must guarantee that no buffer overflow exceptions occur if buffers are sized according to the results of this method's calculations.
Examples
The following code example determines the number of bytes required to encode a character array, encodes the characters, and displays the resulting bytes.
Imports System.Text
Public Class Example
Private Shared outputBlock As System.Windows.Controls.TextBlock
Public Shared Sub Demo(ByVal outBlock As System.Windows.Controls.TextBlock)
outputBlock = outBlock
' The characters to encode:
' 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 myChars() As Char = {"z"c, "a"c, ChrW(&H306), ChrW(&H1FD), ChrW(&H3B2), ChrW(&HD8FF), ChrW(&HDCFF)}
' Get different encodings.
Dim u8 As Encoding = Encoding.UTF8
Dim u16LE As Encoding = Encoding.Unicode
Dim u16BE As Encoding = Encoding.BigEndianUnicode
' Encode the entire array, and print out the counts and the resulting bytes.
PrintCountsAndBytes(myChars, u8)
PrintCountsAndBytes(myChars, u16LE)
PrintCountsAndBytes(myChars, u16BE)
End Sub
Public Shared Sub PrintCountsAndBytes(ByVal chars() As Char, ByVal enc As Encoding)
' Display the name of the encoding used.
outputBlock.Text += String.Format("{0,-30} :", enc.ToString())
' Display the exact byte count.
Dim iBC As Integer = enc.GetByteCount(chars)
outputBlock.Text += String.Format(" {0,-3}", iBC)
' Display the maximum byte count.
Dim iMBC As Integer = enc.GetMaxByteCount(chars.Length)
outputBlock.Text += String.Format(" {0,-3} :", iMBC)
' Encode the array of chars.
Dim bytes As Byte() = enc.GetBytes(chars)
' Display all the encoded bytes.
PrintHexBytes(bytes)
End Sub
Public Shared Sub PrintHexBytes(ByVal bytes() As Byte)
If bytes Is Nothing OrElse bytes.Length = 0 Then
outputBlock.Text &= "<none>" & vbCrLf
Else
Dim i As Integer
For i = 0 To bytes.Length - 1
outputBlock.Text += String.Format("{0:X2} ", bytes(i))
Next i
outputBlock.Text &= vbCrLf
End If
End Sub
End Class
' This example produces the following output.
' System.Text.UTF8Encoding : 12 24 :7A 61 CC 86 C7 BD CE B2 F1 8F B3 BF
' System.Text.UnicodeEncoding : 14 16 :7A 00 61 00 06 03 FD 01 B2 03 FF D8 FF DC
' System.Text.UnicodeEncoding : 14 16 :00 7A 00 61 03 06 01 FD 03 B2 D8 FF DC FF
using System;
using System.Text;
public class Example
{
private static System.Windows.Controls.TextBlock outputBlock;
public static void Demo(System.Windows.Controls.TextBlock outBlock)
{
outputBlock = outBlock;
// The characters to encode:
// 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)
char[] myChars = new char[] { 'z', 'a', '\u0306', '\u01FD', '\u03B2', '\uD8FF', '\uDCFF' };
// Get different encodings.
Encoding u8 = Encoding.UTF8;
Encoding u16LE = Encoding.Unicode;
Encoding u16BE = Encoding.BigEndianUnicode;
// Encode the entire array, and print out the counts and the resulting bytes.
PrintCountsAndBytes(myChars, u8);
PrintCountsAndBytes(myChars, u16LE);
PrintCountsAndBytes(myChars, u16BE);
}
public static void PrintCountsAndBytes(char[] chars, Encoding enc)
{
// Display the name of the encoding used.
outputBlock.Text += String.Format("{0,-30} :", enc.ToString());
// Display the exact byte count.
int iBC = enc.GetByteCount(chars);
outputBlock.Text += String.Format(" {0,-3}", iBC);
// Display the maximum byte count.
int iMBC = enc.GetMaxByteCount(chars.Length);
outputBlock.Text += String.Format(" {0,-3} :", iMBC);
// Encode the array of chars.
byte[] bytes = enc.GetBytes(chars);
// Display all the encoded bytes.
PrintHexBytes(bytes);
}
public static void PrintHexBytes(byte[] bytes)
{
if ((bytes == null) || (bytes.Length == 0))
outputBlock.Text += "<none>" + "\n";
else
{
for (int i = 0; i < bytes.Length; i++)
outputBlock.Text += String.Format("{0:X2} ", bytes[i]);
outputBlock.Text += "\n";
}
}
}
/*
This code produces the following output.
System.Text.UTF8Encoding : 12 24 :7A 61 CC 86 C7 BD CE B2 F1 8F B3 BF
System.Text.UnicodeEncoding : 14 16 :7A 00 61 00 06 03 FD 01 B2 03 FF D8 FF DC
System.Text.UnicodeEncoding : 14 16 :00 7A 00 61 03 06 01 FD 03 B2 D8 FF DC FF
*/
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.