ASCIIEncoding Class

Definition

Namespace:

System.Text

Assembly:

System.Text.Encoding.Extensions.dll

Source:

ASCIIEncoding.cs

Represents an ASCII character encoding of Unicode characters.

public ref class ASCIIEncoding : System::Text::Encoding

public class ASCIIEncoding : System.Text.Encoding

type ASCIIEncoding = class
    inherit Encoding

Public Class ASCIIEncoding
Inherits Encoding

Inheritance

Object

Encoding

ASCIIEncoding

Examples

The following example demonstrates how to encode Unicode characters into ASCII. Notice the loss of data that occurs when your application uses ASCIIEncoding to encode Unicode characters outside of the ASCII range.

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 = L"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 );
}
// The example displays the following output:
//    Original string:
//    This Unicode string contains two characters with codes outside the ASCII code ra
//    nge, Pi (Π) and Sigma (Σ).
//
//    Encoded bytes:
//    [84][104][105][115][32][85][110][105][99][111][100][101][32][115][116][114][105]
//    [110][103][32][99][111][110][116][97][105][110][115][32][116][119][111][32][99][
//    104][97][114][97][99][116][101][114][115][32][119][105][116][104][32][99][111][1
//    00][101][115][32][111][117][116][115][105][100][101][32][116][104][101][32][65][
//    83][67][73][73][32][99][111][100][101][32][114][97][110][103][101][44][32][80][1
//    05][32][40][63][41][32][97][110][100][32][83][105][103][109][97][32][40][63][41]
//    [46]
//
//    Value at position of Pi character: 63
//    Value at position of Sigma character: 63
//
//    Decoded bytes:
//    This Unicode string contains two characters with codes outside the ASCII code ra
//    nge, Pi (?) and Sigma (?).

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);
    }
}
// The example displays the following output:
//    Original string:
//    This Unicode string contains two characters with codes outside the ASCII code ra
//    nge, Pi (Π) and Sigma (Σ).
//
//    Encoded bytes:
//    [84][104][105][115][32][85][110][105][99][111][100][101][32][115][116][114][105]
//    [110][103][32][99][111][110][116][97][105][110][115][32][116][119][111][32][99][
//    104][97][114][97][99][116][101][114][115][32][119][105][116][104][32][99][111][1
//    00][101][115][32][111][117][116][115][105][100][101][32][116][104][101][32][65][
//    83][67][73][73][32][99][111][100][101][32][114][97][110][103][101][44][32][80][1
//    05][32][40][63][41][32][97][110][100][32][83][105][103][109][97][32][40][63][41]
//    [46]
//
//    Value at position of Pi character: 63
//    Value at position of Sigma character: 63
//
//    Decoded bytes:
//    This Unicode string contains two characters with codes outside the ASCII code ra
//    nge, Pi (?) and Sigma (?).

Imports System.Text

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
End Class
' The example displays the following output:
'    Original string:
'    This Unicode string contains two characters with codes outside the ASCII code ra
'    nge, Pi (Π) and Sigma (Σ).
'
'    Encoded bytes:
'    [84][104][105][115][32][85][110][105][99][111][100][101][32][115][116][114][105]
'    [110][103][32][99][111][110][116][97][105][110][115][32][116][119][111][32][99][
'    104][97][114][97][99][116][101][114][115][32][119][105][116][104][32][99][111][1
'    00][101][115][32][111][117][116][115][105][100][101][32][116][104][101][32][65][
'    83][67][73][73][32][99][111][100][101][32][114][97][110][103][101][44][32][80][1
'    05][32][40][63][41][32][97][110][100][32][83][105][103][109][97][32][40][63][41]
'    [46]
'
'    Value at position of Pi character: 63
'    Value at position of Sigma character: 63
'
'    Decoded bytes:
'    This Unicode string contains two characters with codes outside the ASCII code ra
'    nge, Pi (?) and Sigma (?).

Remarks

Encoding is the process of transforming a set of Unicode characters into a sequence of bytes. Decoding is the process of transforming a sequence of encoded bytes into a set of Unicode characters.

ASCIIEncoding corresponds to the Windows code page 20127. Because ASCII is a 7-bit encoding, ASCII characters are limited to the lowest 128 Unicode characters, from U+0000 to U+007F. If you use the default encoder returned by the Encoding.ASCII property or the ASCIIEncoding constructor, characters outside that range are replaced with a question mark (?) before the encoding operation is performed. Because the ASCIIEncoding class supports only a limited character set, the UTF8Encoding, UnicodeEncoding, and UTF32Encoding classes are better suited for globalized applications. The following considerations can help you to decide whether to use ASCIIEncoding:

• Some protocols require ASCII or a subset of ASCII. In these cases ASCII encoding is appropriate.

• If an 8-bit encoding is expected, then ASCII probably isn't the correct choice. Instead, consider using UTF8 instead of ASCII. For the characters U+0000 through U+007F, the results are identical, but all Unicode characters are representable in UTF-8, which avoids data loss.

Caution

ASCIIEncoding does not provide error detection. For security reasons, you should use UTF8Encoding, UnicodeEncoding, or UTF32Encoding and enable error detection.

The GetByteCount method determines how many bytes result in encoding a set of Unicode characters, and the GetBytes method performs the actual encoding.

Likewise, the GetCharCount method determines how many characters result in decoding a sequence of bytes, and the GetChars and GetString methods perform the actual decoding.

Note that the default ASCIIEncoding constructor by itself might not have the appropriate behavior for your application. You might want to consider setting the EncoderFallback or DecoderFallback property to EncoderExceptionFallback or DecoderExceptionFallback to prevent sequences with the 8th bit set. Custom behavior might also be appropriate for these cases.

Constructors

ASCIIEncoding()

Initializes a new instance of the ASCIIEncoding class.

Properties

BodyName	When overridden in a derived class, gets a name for the current encoding that can be used with mail agent body tags. (Inherited from Encoding)
CodePage	When overridden in a derived class, gets the code page identifier of the current Encoding. (Inherited from Encoding)
DecoderFallback	Gets or sets the DecoderFallback object for the current Encoding object. (Inherited from Encoding)
EncoderFallback	Gets or sets the EncoderFallback object for the current Encoding object. (Inherited from Encoding)
EncodingName	When overridden in a derived class, gets the human-readable description of the current encoding. (Inherited from Encoding)
HeaderName	When overridden in a derived class, gets a name for the current encoding that can be used with mail agent header tags. (Inherited from Encoding)
IsBrowserDisplay	When overridden in a derived class, gets a value indicating whether the current encoding can be used by browser clients for displaying content. (Inherited from Encoding)
IsBrowserSave	When overridden in a derived class, gets a value indicating whether the current encoding can be used by browser clients for saving content. (Inherited from Encoding)
IsMailNewsDisplay	When overridden in a derived class, gets a value indicating whether the current encoding can be used by mail and news clients for displaying content. (Inherited from Encoding)
IsMailNewsSave	When overridden in a derived class, gets a value indicating whether the current encoding can be used by mail and news clients for saving content. (Inherited from Encoding)
IsReadOnly	When overridden in a derived class, gets a value indicating whether the current encoding is read-only. (Inherited from Encoding)
IsSingleByte	Gets a value indicating whether the current encoding uses single-byte code points.
Preamble	When overridden in a derived class, returns a span containing the sequence of bytes that specifies the encoding used. (Inherited from Encoding)
WebName	When overridden in a derived class, gets the name registered with the Internet Assigned Numbers Authority (IANA) for the current encoding. (Inherited from Encoding)
WindowsCodePage	When overridden in a derived class, gets the Windows operating system code page that most closely corresponds to the current encoding. (Inherited from Encoding)

Methods

Clone()	When overridden in a derived class, creates a shallow copy of the current Encoding object. (Inherited from Encoding)
Equals(Object)	Determines whether the specified Object is equal to the current instance. (Inherited from Encoding)
GetByteCount(Char*, Int32)	Calculates the number of bytes produced by encoding a set of characters starting at the specified character pointer.
GetByteCount(Char[])	When overridden in a derived class, calculates the number of bytes produced by encoding all the characters in the specified character array. (Inherited from Encoding)
GetByteCount(Char[], Int32, Int32)	Calculates the number of bytes produced by encoding a set of characters from the specified character array.
GetByteCount(ReadOnlySpan<Char>)	Calculates the number of bytes produced by encoding the specified character span.
GetByteCount(String)	Calculates the number of bytes produced by encoding the characters in the specified String.
GetByteCount(String, Int32, Int32)	When overridden in a derived class, calculates the number of bytes produced by encoding a set of characters from the specified string. (Inherited from Encoding)
GetBytes(Char*, Int32, Byte*, Int32)	Encodes a set of characters starting at the specified character pointer into a sequence of bytes that are stored starting at the specified byte pointer.
GetBytes(Char[])	When overridden in a derived class, encodes all the characters in the specified character array into a sequence of bytes. (Inherited from Encoding)
GetBytes(Char[], Int32, Int32)	When overridden in a derived class, encodes a set of characters from the specified character array into a sequence of bytes. (Inherited from Encoding)
GetBytes(Char[], Int32, Int32, Byte[], Int32)	Encodes a set of characters from the specified character array into the specified byte array.
GetBytes(ReadOnlySpan<Char>, Span<Byte>)	Encodes the specified character span into the specified byte span.
GetBytes(String)	When overridden in a derived class, encodes all the characters in the specified string into a sequence of bytes. (Inherited from Encoding)
GetBytes(String, Int32, Int32)	When overridden in a derived class, encodes into an array of bytes the number of characters specified by count in the specified string, starting from the specified index. (Inherited from Encoding)
GetBytes(String, Int32, Int32, Byte[], Int32)	Encodes a set of characters from the specified String into the specified byte array.
GetCharCount(Byte*, Int32)	Calculates the number of characters produced by decoding a sequence of bytes starting at the specified byte pointer.
GetCharCount(Byte[])	When overridden in a derived class, calculates the number of characters produced by decoding all the bytes in the specified byte array. (Inherited from Encoding)
GetCharCount(Byte[], Int32, Int32)	Calculates the number of characters produced by decoding a sequence of bytes from the specified byte array.
GetCharCount(ReadOnlySpan<Byte>)	Calculates the number of characters produced by decoding the specified byte span.
GetChars(Byte*, Int32, Char*, Int32)	Decodes a sequence of bytes starting at the specified byte pointer into a set of characters that are stored starting at the specified character pointer.
GetChars(Byte[])	When overridden in a derived class, decodes all the bytes in the specified byte array into a set of characters. (Inherited from Encoding)
GetChars(Byte[], Int32, Int32)	When overridden in a derived class, decodes a sequence of bytes from the specified byte array into a set of characters. (Inherited from Encoding)
GetChars(Byte[], Int32, Int32, Char[], Int32)	Decodes a sequence of bytes from the specified byte array into the specified character array.
GetChars(ReadOnlySpan<Byte>, Span<Char>)	Decodes the specified byte span into the specified character span.
GetDecoder()	Obtains a decoder that converts an ASCII encoded sequence of bytes into a sequence of Unicode characters.
GetEncoder()	Obtains an encoder that converts a sequence of Unicode characters into an ASCII encoded sequence of bytes.
GetHashCode()	Returns the hash code for the current instance. (Inherited from Encoding)
GetMaxByteCount(Int32)	Calculates the maximum number of bytes produced by encoding the specified number of characters.
GetMaxCharCount(Int32)	Calculates the maximum number of characters produced by decoding the specified number of bytes.
GetPreamble()	When overridden in a derived class, returns a sequence of bytes that specifies the encoding used. (Inherited from Encoding)
GetString(Byte*, Int32)	When overridden in a derived class, decodes a specified number of bytes starting at a specified address into a string. (Inherited from Encoding)
GetString(Byte[])	When overridden in a derived class, decodes all the bytes in the specified byte array into a string. (Inherited from Encoding)
GetString(Byte[], Int32, Int32)	Decodes a range of bytes from a byte array into a string.
GetString(ReadOnlySpan<Byte>)	When overridden in a derived class, decodes all the bytes in the specified byte span into a string. (Inherited from Encoding)
GetType()	Gets the Type of the current instance. (Inherited from Object)
IsAlwaysNormalized()	Gets a value indicating whether the current encoding is always normalized, using the default normalization form. (Inherited from Encoding)
IsAlwaysNormalized(NormalizationForm)	When overridden in a derived class, gets a value indicating whether the current encoding is always normalized, using the specified normalization form. (Inherited from Encoding)
MemberwiseClone()	Creates a shallow copy of the current Object. (Inherited from Object)
ToString()	Returns a string that represents the current object. (Inherited from Object)
TryGetBytes(ReadOnlySpan<Char>, Span<Byte>, Int32)	Encodes into a span of bytes a set of characters from the specified read-only span if the destination is large enough.
TryGetChars(ReadOnlySpan<Byte>, Span<Char>, Int32)	Decodes into a span of chars a set of bytes from the specified read-only span if the destination is large enough.

Extension Methods

GetBytes(Encoding, ReadOnlySequence<Char>)	Encodes the specified ReadOnlySequence<T> into a Byte array using the specified Encoding.
GetBytes(Encoding, ReadOnlySequence<Char>, IBufferWriter<Byte>)	Decodes the specified ReadOnlySequence<T> to bytes using the specified Encoding and writes the result to writer.
GetBytes(Encoding, ReadOnlySequence<Char>, Span<Byte>)	Encodes the specified ReadOnlySequence<T> to bytes using the specified Encoding and outputs the result to bytes.
GetBytes(Encoding, ReadOnlySpan<Char>, IBufferWriter<Byte>)	Encodes the specified ReadOnlySpan<T> to bytes using the specified Encoding and writes the result to writer.
GetChars(Encoding, ReadOnlySequence<Byte>, IBufferWriter<Char>)	Decodes the specified ReadOnlySequence<T> to chars using the specified Encoding and writes the result to writer.
GetChars(Encoding, ReadOnlySequence<Byte>, Span<Char>)	Decodes the specified ReadOnlySequence<T> to chars using the specified Encoding and outputs the result to chars.
GetChars(Encoding, ReadOnlySpan<Byte>, IBufferWriter<Char>)	Decodes the specified ReadOnlySpan<T> to chars using the specified Encoding and writes the result to writer.
GetString(Encoding, ReadOnlySequence<Byte>)	Decodes the specified ReadOnlySequence<T> into a String using the specified Encoding.

See also

• Decoder
• Encoder
• Understanding Encodings