UTF8Encoding Class

Definition

Namespace:

System.Text

Assembly:

System.Text.Encoding.Extensions.dll

Source:

UTF8Encoding.cs

Represents a UTF-8 encoding of Unicode characters.

public ref class UTF8Encoding : System::Text::Encoding

public class UTF8Encoding : System.Text.Encoding

type UTF8Encoding = class
    inherit Encoding

Public Class UTF8Encoding
Inherits Encoding

Inheritance

Object

Encoding

UTF8Encoding

Examples

The following example uses a UTF8Encoding object to encode a string of Unicode characters and store them in a byte array. The Unicode string includes two characters, Pi (U+03A0) and Sigma (U+03A3), that are outside the ASCII character range. When the encoded byte array is decoded back to a string, the Pi and Sigma characters are still present.

using namespace System;
using namespace System::Text;
//using namespace System::Collections;

int main()
{
   // Create a UTF-8 encoding.
   UTF8Encoding^ utf8 = gcnew UTF8Encoding;
   
   // A Unicode string with two characters outside an 8-bit code range.
   String^ unicodeString = L"This Unicode string has 2 characters " +
                           L"outside the ASCII range:\n" +
                           L"Pi (\u03a0), and Sigma (\u03a3).";
   Console::WriteLine("Original string:");
   Console::WriteLine(unicodeString);
   
   // Encode the string.
   array<Byte>^ encodedBytes = utf8->GetBytes(unicodeString );
   Console::WriteLine();
   Console::WriteLine("Encoded bytes:");
   for (int ctr = 0; ctr < encodedBytes->Length; ctr++) {
      Console::Write( "{0:X2} ", encodedBytes[ctr]);
      if ((ctr + 1) % 25 == 0)
         Console::WriteLine();
   }

   Console::WriteLine();
   
   // Decode bytes back to string.
   String^ decodedString = utf8->GetString(encodedBytes);
   Console::WriteLine();
   Console::WriteLine("Decoded bytes:");
   Console::WriteLine(decodedString);
}
// The example displays the following output:
//    Original string:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).
//
//    Encoded bytes:
//    54 68 69 73 20 55 6E 69 63 6F 64 65 20 73 74 72 69 6E 67 20 68 61 73 20 32
//    20 63 68 61 72 61 63 74 65 72 73 20 6F 75 74 73 69 64 65 20 74 68 65 20 41
//    53 43 49 49 20 72 61 6E 67 65 3A 20 0D 0A 50 69 20 28 CE A0 29 2C 20 61 6E
//    64 20 53 69 67 6D 61 20 28 CE A3 29 2E
//
//    Decoded bytes:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).

using System;
using System.Text;

class Example
{
    public static void Main()
    {
        // Create a UTF-8 encoding.
        UTF8Encoding utf8 = new UTF8Encoding();
        
        // A Unicode string with two characters outside an 8-bit code range.
        String unicodeString =
            "This Unicode string has 2 characters outside the " +
            "ASCII range:\n" +
            "Pi (\u03a0), and Sigma (\u03a3).";
        Console.WriteLine("Original string:");
        Console.WriteLine(unicodeString);

        // Encode the string.
        Byte[] encodedBytes = utf8.GetBytes(unicodeString);
        Console.WriteLine();
        Console.WriteLine("Encoded bytes:");
        for (int ctr = 0; ctr < encodedBytes.Length; ctr++) {
            Console.Write("{0:X2} ", encodedBytes[ctr]);
            if ((ctr + 1) %  25 == 0)
               Console.WriteLine();
        }
        Console.WriteLine();
        
        // Decode bytes back to string.
        String decodedString = utf8.GetString(encodedBytes);
        Console.WriteLine();
        Console.WriteLine("Decoded bytes:");
        Console.WriteLine(decodedString);
    }
}
// The example displays the following output:
//    Original string:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).
//
//    Encoded bytes:
//    54 68 69 73 20 55 6E 69 63 6F 64 65 20 73 74 72 69 6E 67 20 68 61 73 20 32
//    20 63 68 61 72 61 63 74 65 72 73 20 6F 75 74 73 69 64 65 20 74 68 65 20 41
//    53 43 49 49 20 72 61 6E 67 65 3A 20 0D 0A 50 69 20 28 CE A0 29 2C 20 61 6E
//    64 20 53 69 67 6D 61 20 28 CE A3 29 2E
//
//    Decoded bytes:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).

Imports System.Text

Class Example
    Public Shared Sub Main()
        ' Create a UTF-8 encoding.
        Dim utf8 As New UTF8Encoding()
        
        ' A Unicode string with two characters outside an 8-bit code range.
        Dim unicodeString As String = _
            "This Unicode string has 2 characters outside the " &
            "ASCII range: " & vbCrLf &
            "Pi (" & ChrW(&h03A0) & "), and Sigma (" & ChrW(&h03A3) & ")."
        Console.WriteLine("Original string:")
        Console.WriteLine(unicodeString)
        
        ' Encode the string.
        Dim encodedBytes As Byte() = utf8.GetBytes(unicodeString)
        Console.WriteLine()
        Console.WriteLine("Encoded bytes:")
        For ctr As Integer = 0 To encodedBytes.Length - 1
            Console.Write("{0:X2} ", encodedBytes(ctr))
            If (ctr + 1) Mod 25 = 0 Then Console.WriteLine
        Next
        Console.WriteLine()
        
        ' Decode bytes back to string.
        Dim decodedString As String = utf8.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 has 2 characters outside the ASCII range:
'    Pi (π), and Sigma (Σ).
'
'    Encoded bytes:
'    54 68 69 73 20 55 6E 69 63 6F 64 65 20 73 74 72 69 6E 67 20 68 61 73 20 32
'    20 63 68 61 72 61 63 74 65 72 73 20 6F 75 74 73 69 64 65 20 74 68 65 20 41
'    53 43 49 49 20 72 61 6E 67 65 3A 20 0D 0A 50 69 20 28 CE A0 29 2C 20 61 6E
'    64 20 53 69 67 6D 61 20 28 CE A3 29 2E
'
'    Decoded bytes:
'    This Unicode string has 2 characters outside the ASCII range:
'    Pi (π), and Sigma (Σ).

The following example uses the same string as the previous example, except that it writes the encoded bytes to a file and prefixes the byte stream with a byte order mark (BOM). It then reads the file in two different ways: as a text file by using a StreamReader object; and as a binary file. As you would expect, neither newly-read string includes the BOM.

using System;
using System.IO;
using System.Text;

public class Example
{
   public static void Main()
   {
        // Create a UTF-8 encoding that supports a BOM.
        Encoding utf8 = new UTF8Encoding(true);

        // A Unicode string with two characters outside an 8-bit code range.
        String unicodeString =
            "This Unicode string has 2 characters outside the " +
            "ASCII range:\n" +
            "Pi (\u03A0)), and Sigma (\u03A3).";
        Console.WriteLine("Original string:");
        Console.WriteLine(unicodeString);
        Console.WriteLine();

        // Encode the string.
        Byte[] encodedBytes = utf8.GetBytes(unicodeString);
        Console.WriteLine("The encoded string has {0} bytes.",
                          encodedBytes.Length);
        Console.WriteLine();

        // Write the bytes to a file with a BOM.
        var fs = new FileStream(@".\UTF8Encoding.txt", FileMode.Create);
        Byte[] bom = utf8.GetPreamble();
        fs.Write(bom, 0, bom.Length);
        fs.Write(encodedBytes, 0, encodedBytes.Length);
        Console.WriteLine("Wrote {0} bytes to the file.", fs.Length);
        fs.Close();
        Console.WriteLine();

        // Open the file using StreamReader.
        var sr = new StreamReader(@".\UTF8Encoding.txt");
        String newString = sr.ReadToEnd();
        sr.Close();
        Console.WriteLine("String read using StreamReader:");
        Console.WriteLine(newString);
        Console.WriteLine();

        // Open the file as a binary file and decode the bytes back to a string.
        fs = new FileStream(@".\UTF8Encoding.txt", FileMode.Open);
        Byte[] bytes = new Byte[fs.Length];
        fs.Read(bytes, 0, (int)fs.Length);
        fs.Close();

        String decodedString = utf8.GetString(bytes);
        Console.WriteLine("Decoded bytes:");
        Console.WriteLine(decodedString);
   }
}
// The example displays the following output:
//    Original string:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).
//
//    The encoded string has 88 bytes.
//
//    Wrote 91 bytes to the file.
//
//    String read using StreamReader:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).
//
//    Decoded bytes:
//    This Unicode string has 2 characters outside the ASCII range:
//    Pi (π), and Sigma (Σ).

Imports System.IO
Imports System.Text

Class Example
    Public Shared Sub Main()
        ' Create a UTF-8 encoding that supports a BOM.
        Dim utf8 As New UTF8Encoding(True)
        
        ' A Unicode string with two characters outside an 8-bit code range.
        Dim unicodeString As String = _
            "This Unicode string has 2 characters outside the " &
            "ASCII range: " & vbCrLf &
            "Pi (" & ChrW(&h03A0) & "), and Sigma (" & ChrW(&h03A3) & ")."
        Console.WriteLine("Original string:")
        Console.WriteLine(unicodeString)
        Console.WriteLine()
        
        ' Encode the string.
        Dim encodedBytes As Byte() = utf8.GetBytes(unicodeString)
        Console.WriteLine("The encoded string has {0} bytes.",
                          encodedBytes.Length)
        Console.WriteLine()
        
        ' Write the bytes to a file with a BOM.
        Dim fs As New FileStream(".\UTF8Encoding.txt", FileMode.Create)
        Dim bom() As Byte = utf8.GetPreamble()
        fs.Write(bom, 0, bom.Length)
        fs.Write(encodedBytes, 0, encodedBytes.Length)
        Console.WriteLine("Wrote {0} bytes to the file.", fs.Length)
        fs.Close()
        Console.WriteLine()
        
        ' Open the file using StreamReader.
        Dim sr As New StreamReader(".\UTF8Encoding.txt")
        Dim newString As String = sr.ReadToEnd()
        sr.Close()
        Console.WriteLine("String read using StreamReader:")
        Console.WriteLine(newString)
        Console.WriteLine()
        
        ' Open the file as a binary file and decode the bytes back to a string.
        fs = new FileStream(".\UTF8Encoding.txt", FileMode.Open)
        Dim bytes(fs.Length - 1) As Byte
        fs.Read(bytes, 0, fs.Length)
        fs.Close()

        Dim decodedString As String = utf8.GetString(bytes)
        Console.WriteLine("Decoded bytes:")
        Console.WriteLine(decodedString)
    End Sub
End Class
' The example displays the following output:
'    Original string:
'    This Unicode string has 2 characters outside the ASCII range:
'    Pi (π), and Sigma (Σ).
'
'    The encoded string has 88 bytes.
'
'    Wrote 91 bytes to the file.
'
'    String read using StreamReader:
'    This Unicode string has 2 characters outside the ASCII range:
'    Pi (π), and Sigma (Σ).
'
'    Decoded bytes:
'    This Unicode string has 2 characters outside the ASCII range:
'    Pi (π), and Sigma (Σ).

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.

UTF-8 is a Unicode encoding that represents each code point as a sequence of one to four bytes. Unlike the UTF-16 and UTF-32 encodings, the UTF-8 encoding does not require "endianness"; the encoding scheme is the same regardless of whether the processor is big-endian or little-endian. UTF8Encoding corresponds to the Windows code page 65001. For more information about the UTFs and other encodings supported by System.Text, see Character Encoding in the .NET Framework.

You can instantiate a UTF8Encoding object in a number of ways, depending on whether you want to it to provide a byte order mark (BOM) and whether you want to enable error detection. The following table lists the constructors and the Encoding property that return a UTF8Encoding object.

Member	BOM	Error detection
Encoding.UTF8	Yes	No (Replacement fallback)
UTF8Encoding.UTF8Encoding()	No	No (Replacement fallback)
UTF8Encoding.UTF8Encoding(Boolean)	Configurable	No (Replacement fallback)
UTF8Encoding.UTF8Encoding(Boolean, Boolean)	Configurable	Configurable

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.

For an encoder or decoder that is able to save state information when encoding or decoding data that spans multiple blocks (such as string of 1 million characters that is encoded in 100,000-character segments), use the GetEncoder and GetDecoder properties, respectively.

Optionally, the UTF8Encoding object provides a byte order mark (BOM), which is an array of bytes that can be prefixed to the beginning of the byte stream that results from the encoding process. If a UTF-8 encoded byte stream is prefaced with a byte order mark (BOM), it helps the decoder determine the byte order and the transformation format or UTF. Note, however, that the Unicode Standard neither requires nor recommends a BOM in UTF-8 encoded streams. For more information on byte order and the byte order mark, see The Unicode Standard at the Unicode home page.

If the encoder is configured to provide a BOM, you can retrieve it by calling the GetPreamble method; otherwise, the method returns an empty array. Note that, even if a UTF8Encoding object is configured for BOM support, you must include the BOM at the beginning of the encoded byte stream as appropriate; the encoding methods of the UTF8Encoding class do not do this automatically.

Caution

To enable error detection and to make the class instance more secure, you should call the UTF8Encoding(Boolean, Boolean) constructor and set the throwOnInvalidBytes parameter to true. With error detection enabled, a method that detects an invalid sequence of characters or bytes throws an ArgumentException exception. Without error detection, no exception is thrown, and the invalid sequence is generally ignored.

Note

The state of a UTF-8 encoded object is not preserved if the object is serialized and deserialized using different .NET Framework versions.

Constructors

UTF8Encoding()	Initializes a new instance of the UTF8Encoding class.
UTF8Encoding(Boolean)	Initializes a new instance of the UTF8Encoding class. A parameter specifies whether to provide a Unicode byte order mark.
UTF8Encoding(Boolean, Boolean)	Initializes a new instance of the UTF8Encoding class. Parameters specify whether to provide a Unicode byte order mark and whether to throw an exception when an invalid encoding is detected.

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	When overridden in a derived class, gets a value indicating whether the current encoding uses single-byte code points. (Inherited from Encoding)
Preamble	Gets a Unicode byte order mark encoded in UTF-8 format, if this object is configured to supply one.
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 UTF8Encoding object.
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 a UTF-8 encoded sequence of bytes into a sequence of Unicode characters.
GetEncoder()	Obtains an encoder that converts a sequence of Unicode characters into a UTF-8 encoded sequence of bytes.
GetHashCode()	Returns the hash code for the current instance.
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()	Returns a Unicode byte order mark encoded in UTF-8 format, if the UTF8Encoding encoding object is configured to supply one.
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