Extended Unix Code

EUC-CN

MIME / IANA	GB2312
Alias(es)	csGB2312
Language(s)	Simplified Chinese, English, Russian
Standard	GB 2312 (1980)
Classification	Extended ASCII, Variable-width encoding, CJK encoding, EUC
Extends	US-ASCII
Extensions	748, GBK, GB 18030, x-mac-chinesesimp
Transforms / Encodes	GB 2312
Succeeded by	GBK, GB 18030

EUC-CN[1] is the usual encoded form of the GB 2312 standard for simplified Chinese characters. Unlike the case of Japanese JIS X 0208 and ISO-2022-JP, GB 2312 is not normally used in a 7-bit ISO 2022 code version,[lower-alpha 1] although a variant form called HZ (which delimits GB 2312 text with ASCII sequences) was sometimes used on USENET.

An ASCII character is represented in its usual encoding. A character from GB 2312 is represented by two bytes, both from the range 0xA1–0xFE.

EUC-JP

MIME / IANA	EUC-JP
Alias(es)	Unixized JIS (UJIS), csEUCPkdFmtJapanese
Language(s)	Japanese, English, Russian
Classification	Extended ISO 646, Variable-width encoding, CJK encoding, EUC
Extends	US-ASCII or ISO 646:JP
Transforms / Encodes	JIS X 0208, JIS X 0212, JIS X 0201
Succeeded by	EUC-JISx0213

EUC-JP is a variable-width encoding used to represent the elements of three Japanese character set standards, namely JIS X 0208, JIS X 0212, and JIS X 0201. Other names for this encoding include Unixized JIS (or UJIS) and AT&T JIS.[3] 0.1% of all web pages use EUC-JP since August 2018,[4] while 3.2% of Japanese web sites use this encoding (less used than Shift JIS, or UTF-8). It is called Code page 954 by IBM.[5][6] Microsoft has two code page numbers for this encoding (51932 and 20932).

This encoding scheme allows the easy mixing of 7-bit ASCII and 8-bit Japanese without the need for the escape characters employed by ISO-2022-JP, which is based on the same character set standards, and without ASCII bytes appearing as trail bytes (unlike Shift JIS).

A related and partially compatible encoding, called EUC-JISx0213 or EUC-JIS-2004, encodes JIS X 0201 and JIS X 0213[7] (similarly to Shift_JISx0213, its Shift_JIS-based counterpart).

Compared to EUC-CN or EUC-KR, EUC-JP did not become as widely adopted on PC and Macintosh systems in Japan, which used Shift JIS or its extensions (Windows code page 932 on Microsoft Windows, and MacJapanese on classic Mac OS), although it became heavily used by Unix or Unix-like operating systems (except for HP-UX). Therefore, whether Japanese web sites use EUC-JP or Shift_JIS often depends on what OS the author uses.

Vendor extensions to EUC-JP were usually allocated within the individual code sets,[8] as opposed to using invalid EUC sequences (as in popular extensions of EUC-CN and EUC-KR).

Characters are encoded as follows:

• As an EUC/ISO 2022 compliant encoding, the C0 control characters, space and DEL are represented as in ASCII.
• A graphical character from ASCII (code set 0) is represented as its usual one-byte representation, in the range 0x21 – 0x7E. While some variants of EUC-JP encode the lower half of JIS X 0201 here, most encode ASCII,[9] including the W3C/WHATWG Encoding standard used by HTML5,[10] and so does EUC-JIS-2004.[7] While this means that 0x5C is typically mapped to Unicode as U+005C REVERSE SOLIDUS (the ASCII backslash), U+005C may be displayed as a Yen sign by certain Japanese-locale fonts, e.g. on Microsoft Windows, for compatibility with the lower half of JIS X 0201.[11][12]
• A character from JIS X 0208 (code set 1) is represented by two bytes, both in the range 0xA1 – 0xFE. This differs from the ISO-2022-JP representation by having the high bit set. This code set may also contain vendor extensions in some EUC-JP variants. In EUC-JIS-2004, the first plane of JIS X 0213 is encoded here, which is effectively a superset of standard JIS X 0208.[7]
• A character from the upper half of JIS X 0201 (half-width kana, code set 2) is represented by two bytes, the first being 0x8E, the second being the usual JIS X 0201 representation in the range 0xA1 – 0xDF. This set may contain IBM vendor extensions in some variants.
• A character from JIS X 0212 (code set 3) is represented in EUC-JP by three bytes, the first being 0x8F, the following two being in the range 0xA1–0xFE, i.e. with the high bit set. In addition to standard JIS X 0212, code set 3 of some EUC-JP variants may also contain extensions in rows 83 and 84 to represent characters from IBM's Shift JIS extensions which lack standard JIS X 0212 mappings, which may be coded in either of two layouts, one defined by IBM themselves and one defined by the OSF.[8][13] In EUC-JIS-2004, the second plane of JIS X 0213 is encoded here,[7] which does not collide with the allocated rows in standard JIS X 0212.[14] Some implementations of EUC-JIS-2004, such as the one used by Python, allow both JIS X 0212 and JIS X 0213 plane 2 characters in this set.[14]

EUC-KR

EUC-KR code structure
MIME / IANA	EUC-KR
Alias(es)	Wansung, IBM-970
Language(s)	Korean, English, Russian
Standard	KS X 2901 (KS C 5861)
Classification	Extended ISO 646, Variable-width encoding, CJK encoding, EUC
Extends	US-ASCII or ISO 646:KR
Extensions	Mac OS Korean, IBM-949, Unified Hangul Code (Windows-949)
Transforms / Encodes	KS X 1001
Succeeded by	Unified Hangul Code (web standards)

EUC-KR is a variable-width encoding to represent Korean text using two coded character sets, KS X 1001 (formerly KS C 5601)[15][16] and either ISO 646:KR (KS X 1003, formerly KS C 5636) or US-ASCII, depending on variant. KS X 2901 (formerly KS C 5861) stipulates the encoding and RFC 1557 dubbed it as EUC-KR.

A character drawn from KS X 1001 (G1, code set 1) is encoded as two bytes in GR (0xA1–0xFE) and a character from KS X 1003 or US-ASCII (G0, code set 0) takes one byte in GL (0x21–0x7E).

When used with ASCII, it is called Code page 970 by IBM.[17][18][19] It is known as Code page 51949 by Microsoft.[20] It is usually referred to as Wansung (Korean: 완성, romanized: Wanseong, lit. 'precomposed[21]') in the Republic of Korea.

A common extension of EUC-KR is the Unified Hangul Code (통합형 한글 코드, Tonghabhyeong Hangeul Kodeu,[22] or 통합 완성형, Tonghab Wansunghyung), which is the default Korean codepage on Microsoft Windows (code page 949, numbered 1363 by IBM). The W3C/WHATWG Encoding Standard used by HTML5 incorporates the Unified Hangul Code extensions into its definition of EUC-KR.[23] Other EUC-KR compatible extensions include the Mac OS Korean encoding, used by the classic Mac OS. IBM's code page 949 is yet another, unrelated, EUC-KR extension. Similarly to the EUC-CN extensions described above, these extensions do not conform to the EUC structure.

As of June 2020, 0.1% of all web pages globally use EUC-KR,[4] which is misleading as 18.1% of South Korean web pages use (only country the encoding is meant for),[24] while only 8.9% of web pages using Korean language (making UTF-8 less popular in South Korea than in (seemingly) all countries of the world).[25] Including extensions, it is the most widely used legacy character encoding in Korea on all three major platforms (Unix-like OS, Windows and macOS), but its use has been very slowly decreasing as UTF-8 gains popularity, especially on Linux and macOS.

As with most other encodings, UTF-8 is now preferred for new use, solving problems with consistency between platforms and vendors.

EUC-TW is a variable-width encoding that supports US-ASCII and 16 planes of CNS 11643, each of which is 94x94. It is a rarely used encoding for traditional Chinese characters as used in Taiwan. Big5 is much more common.

• As an EUC/ISO 2022 encoding, the C0 control characters, ASCII space and DEL are encoded as in ASCII.
• A graphical character from US-ASCII (G0, code set 0) is encoded in GL as its usual single byte representation (0x21–0x7E).
• A character from CNS 11643 plane 1 (code set 1) is encoded as two bytes in GR (0xA1–0xFE).
• A character in plane 1 through 16 of CNS 11643 (code set 2) is encoded as four bytes:
  • The first byte is always 0x8E (Single Shift 2).
  • The second byte (0xA1–0xB0) indicates the plane, the number of which is obtained by subtracting 0xA0 from that byte.
  • The third and fourth bytes are in GR (0xA1–0xFE).

Note that the plane 1 of CNS 11643 is encoded twice as code set 1 and a part of code set 2.

UTF-8 is becoming more common than EUC-TW, as with most code pages.

The encodings described above (using bytes in 0x21–0x7E for code set 0, bytes in 0xA1–0xFE for code set 1, 0x8E followed by bytes in 0xA1–0xFE for code set 2 and 0x8F followed by bytes in 0xA1–0xFE for code set 3) are in a variable-width form referred to as the EUC packed format. This is the form usually labelled as EUC.[3]

Internal processing may make use of a fixed-length alternative form called the EUC complete two-byte format. This represents:[3]

• Code set 0 as two bytes in the range 0x21–0x7E (except that the first may be 0x00).
• Code set 1 as two bytes in the range 0xA0–0xFF (except that the first may be 0x80).
• Code set 2 as a byte in the range 0x20–0x7E (or 0x00) followed by a byte in the range 0xA0–0xFF.
• Code set 3 as a byte in the range 0xA0–0xFF (or 0x80) followed by a byte in the range 0x21–0x7E.

Initial bytes of 0x00 and 0x80 are used in cases where the code set uses only one byte. There is also a four-byte fixed-length format.[3] These fixed-length forms are suited to internal processing and are not usually encountered in interchange.

EUC-JP is registered with the IANA in both formats, the packed format as "EUC-JP" or "csEUCPkdFmtJapanese" and the fixed width format as "csEUCFixWidJapanese".[26] Only the packed format is included in the WHATWG Encoding Standard used by HTML5.[27]

• CJK
• Japanese language and computers
• Korean language and computers
• Chinese character encoding

• EUC-JP codeset table (minus the ASCII and halfwidth parts)
• Code Page Identifiers
• GB18030-2000 – The New Chinese National Standard
• The New Generation of Pre-Press Software in China – mentions the 748 code
• Description of the EUC-TW code (in Chinese)
• Manual page of EUC-JISX0213 in the Perl Encode module
• International Register of Coded Character Sets to be Used With Escape Sequence – section 2.4 (p.14f.) with the coded character sets of China, Japan, South Korea, North Korea and Taiwan (ISO/IEC)
• Chinese, Japanese, and Korean character set standards and encoding systems