You may also need to check that your server is serving documents with the right HTTP declarations, since it will otherwise override the in-document information see below. Web pages must be able to communicate seamlessly with back-end scripts, databases, and such.
These, of course, all work best with UTF-8, too. Developers can find a detailed set of things to consider in the article Migrating to Unicode. An HTML page can only be in one encoding. You cannot encode different parts of a document in different encodings. A Unicode-based encoding such as UTF-8 can support many languages and can accommodate pages and forms in any mixture of those languages.
Its use also eliminates the need for server-side logic to individually determine the character encoding for each page served or each incoming form submission. This significantly reduces the complexity of dealing with a multilingual site or application.
A Unicode encoding also allows many more languages to be mixed on a single page than any other choice of encoding. Any barriers to using Unicode are very low these days. Of these three, only UTF-8 should be used for Web content. Conformance checkers may advise authors against using legacy encodings.
Authoring tools should default to using UTF-8 for newly-created documents. Any character encoding declaration in the HTTP header will override declarations inside the page. If the HTTP header declares an encoding that is not the same as the one you want to use for your content this will cause a problem unless you are able to change the server settings.
You may not have control over the declarations that come with the HTTP header, and may have to contact the people who manage the server for help.
On the other hand there are sometimes ways you can fix things on the server if you have limited access to server setup files or are generating pages using scripting languages. This is the default encoding used by Windows systems in most western countries. This means that text data produced by software running on such systems by default will use the Windows encoding, unless explicitly set to use a different one.
Some software lets the user choose which encoding to use, some is set to use a specific encoding rather than the default, and some leaves it up to the system itself. Windows is a single-byte encoding, which means that each character is encoded as a single byte, the same as with ASCII.
UTF-8 is an encoding from the Unicode standard. This means that each character uses at least 8 bits for its code point, but some may use more. As with Windows, the first code points are identical to ASCII, but above that the two encodings differ considerably. While Windows only contains code points altogether, UTF-8 has code points for the entire Unicode character set.
The way this is handled is to define some of the byte values above as prefixes for further byte values. Because the C2 byte is designed as a prefix byte, this opens an additional 2-byte code points with C2 as the first byte. This design means that most of the common characters used in western languages only take up a single byte of space, while the multi-byte encodings are used less frequently.
MaxCharCount or DecoderFallback. MaxCharCount property, which returns the maximum possible number of characters that the best-fit, replacement, or exception fallback can return to replace a single character.
For a custom exception fallback, its value is zero. CreateFallbackBuffer or DecoderFallback. The method is called by the encoder when it encounters the first character that it is unable to successfully encode, or by the decoder when it encounters the first byte that it is unable to successfully decode. To implement a custom fallback solution, you must also create a class that inherits from EncoderFallbackBuffer for encoding operations, and from DecoderFallbackBuffer for decoding operations.
CreateFallbackBuffer method is called by the encoder when it encounters the first character that it is not able to encode, and the DecoderFallback. CreateFallbackBuffer method is called by the decoder when it encounters one or more bytes that it is not able to decode.
Each instance represents a buffer that contains the fallback characters that will replace the character that cannot be encoded or the byte sequence that cannot be decoded.
The EncoderFallbackBuffer. Fallback or DecoderFallbackBuffer. Fallback method. Fallback is called by the encoder to provide the fallback buffer with information about the character that it cannot encode. Because the character to be encoded may be a surrogate pair, this method is overloaded. One overload is passed the character to be encoded and its index in the string.
The second overload is passed the high and low surrogate along with its index in the string. The DecoderFallbackBuffer. Fallback method is called by the decoder to provide the fallback buffer with information about the bytes that it cannot decode.
This method is passed an array of bytes that it cannot decode, along with the index of the first byte. The fallback method should return true if the fallback buffer can supply a best-fit or replacement character or characters; otherwise, it should return false.
For an exception fallback, the fallback method should throw an exception. GetNextChar method, which is called repeatedly by the encoder or decoder to get the next character from the fallback buffer.
Remaining or DecoderFallbackBuffer. Remaining property, which returns the number of characters remaining in the fallback buffer. MovePrevious or DecoderFallbackBuffer. MovePrevious method, which moves the current position in the fallback buffer to the previous character. Reset or DecoderFallbackBuffer. Reset method, which reinitializes the fallback buffer.
If the fallback implementation is a best-fit fallback or a replacement fallback, the classes derived from EncoderFallbackBuffer and DecoderFallbackBuffer also maintain two private instance fields: the exact number of characters in the buffer; and the index of the next character in the buffer to return. The following example uses a custom best-fit fallback implementation instead to provide a better mapping of non-ASCII characters. To make this mapping available to the fallback buffer, the CustomMapper instance is passed as a parameter to the CustomMapperFallbackBuffer class constructor.
The dictionary that contains best-fit mappings and that is defined in the CustomMapper instance is available from its class constructor. Its Fallback method returns true if any of the Unicode characters that the ASCII encoder cannot encode are defined in the mapping dictionary; otherwise, it returns false. For each fallback, the private count variable indicates the number of characters that remain to be returned, and the private index variable indicates the position in the string buffer, charsToReturn , of the next character to return.
The following code then instantiates the CustomMapper object and passes an instance of it to the Encoding. The output indicates that the best-fit fallback implementation successfully handles the three non-ASCII characters in the original string. Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services.
Privacy policy. Skip to main content. This browser is no longer supported. Download Microsoft Edge More info. Contents Exit focus mode. How to use character encoding classes in. Important The most common problems in encoding operations occur when a Unicode character cannot be mapped to a particular code page encoding. Note In theory, the Unicode encoding classes provided in. Note Best-fit strategies are not documented in detail. Note You can also implement a custom best-fit fallback mapping for an encoding.
Note You can also implement a replacement class for an encoding. Note You can also implement a custom exception handler for an encoding operation. Is this page helpful? Yes No. Any additional feedback? Skip Submit. Submit and view feedback for This product This page. View all page feedback. Encodes a limited range of characters by using the lower seven bits of a byte. UTF-7 supports protocols such as email and newsgroup.
However, UTF-7 is not particularly secure or robust. In some cases, changing one bit can radically alter the interpretation of an entire UTF-7 string. In other cases, different UTF-7 strings can encode the same text. Represents each Unicode code point as a sequence of one to four bytes. UTF-8 supports 8-bit data sizes and works well with many existing operating systems.
Represents each Unicode code point as a sequence of one or two bit integers. Both little-endian and big-endian byte orders are supported. Represents each Unicode code point as a bit integer.
UTF encoding is used when applications want to avoid the surrogate code point behavior of UTF encoding on operating systems for which encoded space is too important. Single glyphs rendered on a display can still be encoded with more than one UTF character. Provides support for a variety of code pages.
On Windows operating systems, code pages are used to support a specific language or group of languages. For a table that lists the code pages supported by. NET, see the Encoding class. You can retrieve an encoding object for a particular code page by calling the Encoding. GetEncoding Int32 method.
A code page contains code points and is zero-based. In most code pages, code points 0 through represent the ASCII character set, and code points through differ significantly between code pages. For example, code page provides the characters for Latin writing systems, including English, German, and French. The last code points in code page contain the accent characters. Code page provides character codes that are required in the Greek writing system.
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