System.Text.UTF8Encoding Class

Represents a UTF-8 encoding of Unicode characters.

See Also: UTF8Encoding Members


public class UTF8Encoding : Encoding


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. For more information about the UTFs and other encodings supported by System.Text, see Understanding Encodings.

The UTF8Encoding.GetByteCount(Char[], int, int) method determines how many bytes result in encoding a set of Unicode characters, and the UTF8Encoding.GetBytes(string, int, int, Byte[], int) method performs the actual encoding.

Likewise, the UTF8Encoding.GetCharCount(Byte[], int, int) method determines how many characters result in decoding a sequence of bytes, and the UTF8Encoding.GetChars(Byte[], int, int, Char[], int) and UTF8Encoding.GetString(Byte[], int, int) methods perform the actual decoding.

System.Text.UTF8Encoding corresponds to the Windows code page 65001.

The encoder can use the big endian byte order (most significant byte first) or the little endian byte order (least significant byte first). It is generally more efficient to store Unicode characters using the native byte order. For example, it is better to use the little endian byte order on little endian platforms, such as Intel computers.

Optionally, the System.Text.UTF8Encoding object provides a preamble, which is an array of bytes that can be prefixed to the sequence of bytes resulting from the encoding process. If the preamble contains a byte order mark (BOM), it helps the decoder determine the byte order and the transformation format or UTF. The UTF8Encoding.GetPreamble method retrieves an array of bytes that can include the BOM. For more information on byte order and the byte order mark, see The Unicode Standard at the tp://


To enable error detection and to make the class instance more secure, the application should use the UTF8Encoding.#ctor constructor that takes a throwOnInvalidBytes parameter and set that parameter to true. With error detection, a method that detects an invalid sequence of characters or bytes throws a ArgumentException. Without error detection, no exception is thrown, and the invalid sequence is generally ignored.


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

Thread Safety

All public static members of this type are safe for multithreaded operations. No instance members are guaranteed to be thread safe.


Namespace: System.Text
Assembly: mscorlib (in mscorlib.dll)
Assembly Versions: 1.0.5000.0,,