ASCIIEncoding 类
表示 Unicode 字符的 ASCII 字符编码。
**命名空间:**System.Text
**程序集:**mscorlib（在 mscorlib.dll 中）
语法
声明
<SerializableAttribute> _
<ComVisibleAttribute(True)> _
Public Class ASCIIEncoding
Inherits Encoding
用法
Dim instance As ASCIIEncoding
[SerializableAttribute]
[ComVisibleAttribute(true)]
public class ASCIIEncoding : Encoding
[SerializableAttribute]
[ComVisibleAttribute(true)]
public ref class ASCIIEncoding : public Encoding
/** @attribute SerializableAttribute() */
/** @attribute ComVisibleAttribute(true) */
public class ASCIIEncoding extends Encoding
SerializableAttribute
ComVisibleAttribute(true)
public class ASCIIEncoding extends Encoding
备注
编码是一个将一组 Unicode 字符转换为一个字节序列的过程。解码是一个反向操作过程，即将一个编码字节序列转换为一组 Unicode 字符。
Unicode 标准为所有支持脚本中的每个字符分配一个码位（一个数字）。Unicode 转换格式 (UTF) 是一种码位编码方式。Unicode 标准 3.2 版使用下列 UTF：
UTF-8，它将每个码位表示为一个由 1 至 4 个字节组成的序列。
UTF-16，它将每个码位表示为一个由 1 至 2 个 16 位整数组成的序列。
UTF-32，它将每个码位表示为一个 32 位整数。
警告
ASCIIEncoding 不提供错误检测。出于安全原因，建议您使用 UTF8Encoding、UnicodeEncoding 或 UTF32Encoding 并启用错误检测。
提示
ASCIIEncoding 仅支持 U+0000 和 U+007F 之间的 Unicode 字符值。因此，UTF8Encoding、UnicodeEncoding 和 UTF32Encoding 可以更好地适应全球化的应用程序。
GetByteCount 方法确定将有多少字节对 Unicode 字符集进行编码，而 GetBytes 方法将执行实际的编码操作。
同样，GetCharCount 方法确定将有多少字符对字节序列进行解码，而 GetChars 和 GetString 方法执行实际的解码。
ASCIIEncoding 对应于 Windows 代码页 20127。
示例
下面的示例演示了如何将 Unicode 字符编码为 ASCII 字符。请注意，当使用 ASCIIEncoding 对 ASCII 范围外的 Unicode 字符进行编码时，会发生数据丢失。
Imports System
Imports System.Text
Imports Microsoft.VisualBasic.Strings
Class ASCIIEncodingExample
Public Shared Sub Main()
' The encoding.
Dim ascii As New ASCIIEncoding()
' A Unicode string with two characters outside the ASCII code range.
Dim unicodeString As String = _
"This Unicode string contains two characters " & _
"with codes outside the ASCII code range, " & _
"Pi (" & ChrW(928) & ") and Sigma (" & ChrW(931) & ")."
Console.WriteLine("Original string:")
Console.WriteLine(unicodeString)
' Save positions of the special characters for later reference.
Dim indexOfPi As Integer = unicodeString.IndexOf(ChrW(928))
Dim indexOfSigma As Integer = unicodeString.IndexOf(ChrW(931))
' Encode string.
Dim encodedBytes As Byte() = ascii.GetBytes(unicodeString)
Console.WriteLine()
Console.WriteLine("Encoded bytes:")
Dim b As Byte
For Each b In encodedBytes
Console.Write("[{0}]", b)
Next b
Console.WriteLine()
' Notice that the special characters have been replaced with
' the value 63, which is the ASCII character code for '?'.
Console.WriteLine()
Console.WriteLine( _
"Value at position of Pi character: {0}", _
encodedBytes(indexOfPi) _
)
Console.WriteLine( _
"Value at position of Sigma character: {0}", _
encodedBytes(indexOfSigma) _
)
' Decode bytes back to string.
' Notice missing Pi and Sigma characters.
Dim decodedString As String = ascii.GetString(encodedBytes)
Console.WriteLine()
Console.WriteLine("Decoded bytes:")
Console.WriteLine(decodedString)
End Sub 'Main
End Class 'ASCIIEncodingExample
using System;
using System.Text;
class ASCIIEncodingExample {
public static void Main() {
// The encoding.
ASCIIEncoding ascii = new ASCIIEncoding();
// A Unicode string with two characters outside the ASCII code range.
String unicodeString =
"This Unicode string contains two characters " +
"with codes outside the ASCII code range, " +
"Pi (\u03a0) and Sigma (\u03a3).";
Console.WriteLine("Original string:");
Console.WriteLine(unicodeString);
// Save positions of the special characters for later reference.
int indexOfPi = unicodeString.IndexOf('\u03a0');
int indexOfSigma = unicodeString.IndexOf('\u03a3');
// Encode string.
Byte[] encodedBytes = ascii.GetBytes(unicodeString);
Console.WriteLine();
Console.WriteLine("Encoded bytes:");
foreach (Byte b in encodedBytes) {
Console.Write("[{0}]", b);
}
Console.WriteLine();
// Notice that the special characters have been replaced with
// the value 63, which is the ASCII character code for '?'.
Console.WriteLine();
Console.WriteLine(
"Value at position of Pi character: {0}",
encodedBytes[indexOfPi]
);
Console.WriteLine(
"Value at position of Sigma character: {0}",
encodedBytes[indexOfSigma]
);
// Decode bytes back to string.
// Notice missing Pi and Sigma characters.
String decodedString = ascii.GetString(encodedBytes);
Console.WriteLine();
Console.WriteLine("Decoded bytes:");
Console.WriteLine(decodedString);
}
}
using namespace System;
using namespace System::Collections;
using namespace System::Text;
int main()
{
// The encoding.
ASCIIEncoding^ ascii = gcnew ASCIIEncoding;
// A Unicode string with two characters outside the ASCII code range.
String^ unicodeString = "This Unicode String* contains two characters with codes outside the ASCII code range, Pi (\u03a0) and Sigma (\u03a3).";
Console::WriteLine( "Original String*:" );
Console::WriteLine( unicodeString );
// Save positions of the special characters for later reference.
int indexOfPi = unicodeString->IndexOf( L'\u03a0' );
int indexOfSigma = unicodeString->IndexOf( L'\u03a3' );
// Encode string.
array<Byte>^encodedBytes = ascii->GetBytes( unicodeString );
Console::WriteLine();
Console::WriteLine( "Encoded bytes:" );
IEnumerator^ myEnum = encodedBytes->GetEnumerator();
while ( myEnum->MoveNext() )
{
Byte b = safe_cast<Byte>(myEnum->Current);
Console::Write( "->Item[ {0}]", b );
}
Console::WriteLine();
// Notice that the special characters have been replaced with
// the value 63, which is the ASCII character code for '?'.
Console::WriteLine();
Console::WriteLine( "Value at position of Pi character: {0}", encodedBytes[ indexOfPi ] );
Console::WriteLine( "Value at position of Sigma character: {0}", encodedBytes[ indexOfSigma ] );
// Decode bytes back to string.
// Notice missing Pi and Sigma characters.
String^ decodedString = ascii->GetString( encodedBytes );
Console::WriteLine();
Console::WriteLine( "Decoded bytes:" );
Console::WriteLine( decodedString );
}
import System.*;
import System.Text.*;
import System.Byte;
class ASCIIEncodingExample
{
public static void main(String[] args)
{
// The encoding.
ASCIIEncoding ascii = new ASCIIEncoding();
// A Unicode string with two characters outside the ASCII code range.
String unicodeString = "This Unicode string contains two characters "
+ "with codes outside the ASCII code range, "
+ "Pi (\u03a0) and Sigma (\u03a3).";
Console.WriteLine("Original string:");
Console.WriteLine(unicodeString);
// Save positions of the special characters for later reference.
int indexOfPi = unicodeString.IndexOf('\u03a0');
int indexOfSigma = unicodeString.IndexOf('\u03a3');
// Encode string.
ubyte encodedBytes[] = ascii.GetBytes(unicodeString);
Console.WriteLine();
Console.WriteLine("Encoded bytes:");
for(int iCtr = 0; iCtr < encodedBytes.length; iCtr++) {
ubyte b = encodedBytes[iCtr];
Console.Write("[{0}]", String.valueOf((Byte)b));
}
Console.WriteLine();
// Notice that the special characters have been replaced with
// the value 63, which is the ASCII character code for '?'.
Console.WriteLine();
Console.WriteLine("Value at position of Pi character: {0}",
encodedBytes.get_Item(indexOfPi));
Console.WriteLine("Value at position of Sigma character: {0}",
encodedBytes.get_Item(indexOfSigma));
// Decode bytes back to string.
// Notice missing Pi and Sigma characters.
String decodedString = ascii.GetString((ubyte[])encodedBytes);
Console.WriteLine();
Console.WriteLine("Decoded bytes:");
Console.WriteLine(decodedString);
} //main
} //ASCIIEncodingExample
继承层次结构
System.Object
System.Text.Encoding
System.Text.ASCIIEncoding
线程安全
此类型的任何公共静态（Visual Basic 中的 Shared）成员都是线程安全的，但不保证所有实例成员都是线程安全的。
平台
Windows 98、Windows 2000 SP4、Windows CE、Windows Millennium Edition、Windows Mobile for Pocket PC、Windows Mobile for Smartphone、Windows Server 2003、Windows XP Media Center Edition、Windows XP Professional x64 Edition、Windows XP SP2、Windows XP Starter Edition
.NET Framework 并不是对每个平台的所有版本都提供支持。有关受支持版本的列表，请参见系统要求。
版本信息
.NET Framework
受以下版本支持：2.0、1.1、1.0
.NET Compact Framework
受以下版本支持：2.0、1.0