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GB 18030

GB 18030 encoding layout. "Half codes" indicates codes used in pairs as four-byte codes.
MIME / IANA	GB18030
Alias(es)	Code page 54936
Languages	International, but primarily meant forChinese
Standard	GB 18030-2022, GB 18030-2005, GB 18030-2000
Classification	Unicode Transformation Format,extended ASCII,[a]variable-width encoding,CJK encoding
Extends	EUC-CN,GBK
Transforms / Encodes	ISO 10646 (Unicode)
Preceded by	GBK,GB2312
^Not in the strictest sense of the term, as ASCII bytes can appear as trail bytes.

GB 18030 is aChinese government standard, described asInformation Technology — Chinese coded character set and defines the required language and character support necessary for software inChina.GB18030 is the registered Internet name for the officialcharacter set of thePeople's Republic of China (PRC) supersedingGB2312.^[1] As aUnicode Transformation Format^[a] (i.e. an encoding of allUnicode code points), GB18030 supports bothsimplified andtraditional Chinese characters. It is also compatible with legacy encodings includingGB/T 2312,CP936,^[b] andGBK 1.0.

TheUnicode Consortium has warned implementers that the latest version of this Chinese standard,GB 18030-2022, introduces what they describe as "disruptive changes" from the previous version GB 18030-2005 "involving 33 different characters and 55 code positions".^[2] GB 18030-2022 was enforced from 1 August 2023.^[3] It has been implemented inICU 73.2; and in Java 21,^[4] andbackported to older Java 8, 11, 17 (LTS releases) and 20.0.2.^[5]

In addition to the encoding method, this standard contains requirements about which additional scripts and languages should be represented, and to whom this standard is applicable.^[6] This standard however does not define the officialcharacter forms for the Chinese characters; this is standardised inList of Commonly Used Standard Chinese Characters.

The GB18030 character set is formally called "Chinese National Standard GB 18030-2005: Information Technology—Chinese coded character set".GB abbreviatesGuójiā Biāozhǔn (国家标准), which meansnational standard in Chinese. The standard was published by the China Standard Press, Beijing, 8 November 2005. Only a portion of the standard is mandatory.^[6] Since 1 May 2006, support for the mandatory subset is officially required for all software products sold in the PRC.

An older version of the standard, known as "Chinese National Standard GB 18030-2000: Information Technology—Chinese ideograms coded character set for information interchange—Extension for the basic set", was published on March 17, 2000. The encoding scheme stays the same in the new version, and the only difference in GB-to-Unicode mapping is that GB 18030-2000 mapped the characterA8 BC (ḿ) to a private use code point U+E7C7, and character81 35 F4 37 (without specifying any glyph) to U+1E3F (ḿ), whereas GB 18030-2005 swaps these two mapping assignments.^[7]: 534 More code points are now associated with characters due to update ofUnicode, especially the appearance ofCJK Unified Ideographs Extension B. Some characters used byethnic minorities in China, such asMongolian characters andTibetan characters (GB 16959-1997 andGB/T 20542-2006), have been added as well, which accounts for the renaming of the standard.

Compared with its ancestors, GB 18030's mapping to Unicode has been modified for the 81 characters that were provisionally assigned a UnicodePrivate Use Area code point (U+E000–F8FF) in GBK 1.0 and that have later been encoded in Unicode.^[8] This is specified in Appendix E of GB 18030.^{[7]: 534 [9]: 499} There are 24 characters in GB 18030-2005 that are still mapped to Unicode PUA.^[10]

In the GB 18030-2022 update, the requirements for characters to be mapped to PUA has been lifted completely and all characters should be mapped to their standard Unicode codepoints. Of these, 18 mappings were updated by position-swapping similar to what happened between GBK and GB 18030. The remaining six kept the two-byte PUA mappings, so that a change to the 4-byte sequence is needed to follow the non-PUA preference.^[11]

The first version of GB 18030, designated GB 18030-2000Information Technology—Chinese coded character set for information interchange — Extension for the basic set, consists of 1-byte and 2-byte encodings, together with 4-byte encoding forCJK Unified Ideographs Extension A matching those in Unicode 3.0. The corresponding Unicode code points of this subset, including provisional private assignments, lie entirely in theBMP. These parts are fully mandatory in GB 18030-2000.^[6]: 2 Most major computer companies had already standardized on some version of Unicode as the primary format for use in their binary formats and OS calls. However, they mostly had only supportedcode points in theBMP originally defined in Unicode 1.0, which supported only 65,536 codepoints and was often encoded in 16 bits asUCS-2. This standard is basically an extension based on GBK with additional characters in CJK Unified Ideographs Extension A.

The second version designated GB 18030-2005Information Technology—Chinese coded character set has the same mandatory subset as GB 18030-2000 of 1-, 2- and 4-byte encodings.^[7]: 3 This version also includes the full CJK Unified Ideographs Extension B in the 4-byte encoding section which is outside the BMP^[10] as a suggestion support requirement.^[14] However, as the inclusion of CJK Unified Ideographs Extension B in a 4-byte region is required to be maintained during information processing, software can no longer get away with treating characters as 16-bit fixed width entities (UCS-2). Therefore, they must either process the data as avariable-width format (as withUTF-8 orUTF-16), which is the most common choice, or move to a larger fixed-width format (i.e.UTF-32). Microsoft made the change from UCS-2 to UTF-16 with Windows 2000. This version matches with Unicode 3.1, and also provided support forHangul (Korean),Mongolian (includingManchu,Clear script,Sibe hergen,Galik),Tai Nuea,Tibetan,Uyghur/Kazakh/Kyrgyz andYi.

The third and latest version, GB 18030-2022Information Technology—Chinese coded character set, mandates the suggestion support part of CJK Unified Ideographs Extension B in GB 18030-2005, along with updates up to Unicode 11.0 includingKangxi Radicals and CJK Unified IdeographsURO, Extension C, D, E and F. Additional languages are also recognized by GB 18030-2022 such as part ofArabic,Tai Le,New Tai Lue,Tai Tham,Lisu, andMiao. GB 18030-2022 also introduces three implementation levels, with the requirement of "all products using this standard should implements Implementation Level 1" that includes 66 new BMP characters in the 4-byte encoding region that were added between Unicode 3.1 and Unicode 11.0. Implementation Level 2 requires the support ofList of Commonly Used Standard Chinese Characters, and Implementation Level 3 requires all other specified regions in the standard.^[11]

From late 2022 to 2023, drafts of a further amendment are to be made to GB 18030-2022 available for public consultation. The current draft updates up to Unicode 15.1 onIdeographic Description Characters, CJK Unified Ideographs URO, Extension A, B, C, G, H and I.^[15][16][17] Originally, in late 2022, it would have placed 897 newsinographic characters in Plane 10 (hexadecimal: 0A), ayet-untitled astral Unicode plane, for citizen real-name certification in China, but eventually therepertoire (reduced to 622 characters after expert review) was fast-tracked into Unicode 15.1 in September 2023, as theCJK Unified Ideographs Extension I block.^[18] Following this, the amendment draft was modified to use the Extension I code points.^[17]

GB 18030 defines a one (ASCII), two (extended GBK), or four-byte (UTF) encoding. The two-byte codes are defined in a lookup table, while the four-byte codes are defined sequentially (hence algorithmically) to fill otherwise unencoded parts inUCS. GB 18030 inherits the bad aspects ofGBK, most notably needing special code to safely find ASCII characters in a GB18030 sequence.

The one- and two-byte code points are essentiallyGBK with the euro sign, PUA mappings for unassigned/user-defined points, and vertical punctuations. The four byte scheme can be thought of as consisting of two units, each of two bytes. Each unit has a similar format to a GBK two byte character but with a range of values for the second byte of 0x30–0x39 (theASCII codes for decimal digits). The first byte has the range 0x81 to 0xFE, as before. This means that a string-search routine that is safe for GBK should also be reasonably^{[clarification needed]} safe for GB18030 (in much the same way that a basicbyte-oriented search routine is reasonably safe forEUC).

This gives a total of 1,587,600 (126×10×126×10) possible 4-byte sequences, which is easily sufficient to coverUnicode's 1,112,064 (17×65536 − 2048 surrogates) assigned, reserved, and noncharacter code points.

Unfortunately, to further complicate matters there are no simple rules to translate between a 4-byte sequence and its correspondingcode point. Instead, codes are allocated sequentially (with the first byte containing the most significant part and the last the least significant part)only to Unicode code points that are not mapped in any other manner.^[h] For example:

U+00DE (Þ) → 81 30 89 37U+00DF (ß) → 81 30 89 38U+00E0 (à) → A8 A4U+00E1 (á) → A8 A2U+00E2 (â) → 81 30 89 39U+00E3 (ã) → 81 30 8A 30

An offset table is used in theWHATWG andW3C version of GB 18030 to efficiently translate code points.^[20] ICU^[19] and glibc use similar range definitions to avoid wasting space on large sequential blocks.

This sectionneeds expansion. You can help byadding to it.(October 2016)

GB 18030 has been supported on Windows since the release ofWindows 95, as code page 54936.^[21] Windows 2000 and XP offer a GB18030 Support Package.^[22] The open source PostgreSQL database supports GB18030 through its full support for UTF-8, i.e. by converting it to and from UTF-8. Similarly Microsoft SQL Server supports GB18030 by conversion to and from UTF-16.

More specifically, supporting the GB18030 encoding on Windows means thatCode Page 54936 is supported byMultiByteToWideChar andWideCharToMultiByte. Due to the backward compatibility of the mapping, many files in GB18030 can be actually opened successfully as the legacy Code Page 936, that is GBK, even if the Code Page 54936 is not supported. However, that is only true if the file in question contains only GBK characters. Loading will fail or cause corrupted result if the file contains characters that do not exist in GBK (see§ Mapping for examples).

GNUglibc's gconv, the character codec library used on most Linux distributions, supports GB 18030-2000 since 2.2,^[23] and GB 18030-2005 since 2.14;^[24] glibc notably includes non-PUA mappings for GB 18030-2005 in order to achieve round-trip conversion.^[25] GNUlibiconv, an alternativeiconv implementation frequently used on non-glibc UNIX-like environments likeCygwin, supports GB 18030 since version 1.4.^[26]

As of 2022, "supporting non-Chinese scripts continues to be optional"^[27] (presumably for display/font support only; and in China, since the encoding is a full UTF). The standard is known to support English/ASCII and the "following non-Chinese scripts are recognized by GB 18030-2022: Arabic, Tibetan, Mongolian, Tai Le, New Tai Lue, Tai Tham, Yi, Lisu, Hangul (Korean), and Miao."^[27]

The GB18030 Support Package for Windows XP and Windows 2000 contained SimSun18030.ttc, a TrueType font collection file which combines two Chinese fonts, SimSun-18030 and NSimSun-18030. TheSimSun-18030 font included all the mandatory CJK characters required in GB18030-2000, including characters in the CJK Unified Ideographs and CJK Unified Ideographs Extension A blocks of Unicode 3.0. Since Windows Vista, Windows has included the Simsun and Simsun-ExtB fonts. (Simsun supports CJK characters in the UnicodeBasic Multilingual Plane, while Simsun-ExtB supports most CJK characters in the UnicodeSupplementary Ideographic Plane). These fonts have been updated in subsequent Windows releases to support additional CJK characters. As of 2022, the Simsun-ExtB font supported CJK Unified IdeographExtension B,Extension C andExtension D. For GB 18030-2022, the Simsun-ExtB font was updated to add support for CJK Unified IdeographExtension E andExtension F.^[28] Also, the Simsun-ExtG font was added to Windows 10 and Windows 11 to support CJK characters in CJK Unified IdeographsExtension G,Extension H andExtension I.^[29][30] The Simsun fonts in Windows 10 and Windows 11 support all CJK characters required for GB18030-2022 plus Amendment 1 level 3 conformance.

Microsoft YaHei andDengXian provided by Microsoft were updated in 2023 to match GB 18030-2022 implementation level 2.^[28]

Source Han Sans (and its counterpart Noto Sans CJK) are already compliant with GB 18030-2022 implementation level 2 when the standard update for GB 18030 is announced as of November 2022^[update].Source Han Serif (and its counterpart Noto Serif CJK) however is not compliant at the time, and an update is provided to ensure the font is compliant to implementation level 2. Similarly Microsoft YaHei and PingFang (Apple) require a small number of URO additions that are associated with implementation level 1 in order to become compliant with GB 18030-2022 implementation level 2.^[27]

Other CJK font families like HAN NOM^[31] and Hanazono Mincho^[32] provide wider coverage for Unicode CJK Extension blocks than SimSun-18030 or even SimSun (Founder Extended), but they don't support all code points defined in GB 18030.

• Guobiao code
• CJK characters
• Chinese character encoding
• Comparison of Unicode encodings

• IANA Charset Registration for GB18030
• "English language summary of  – -2000"(PDF). February 16, 2001. Archived fromthe original(PDF) on 2017-02-02.
• Introduction to GB18030 including evolution from GB2312 and GBK (Sun/Internet Archive)
• ICU data
  • GB18030: A mega-codepage (IBM DeveloperWorks)
  • Authoritative mapping table between GB18030-2000 and Unicode
  • ICU Converter Explorer: GB18030
• Unicode charts
  • Unicode CJK Unified Ideographs Extension A (PDF, 1.5 MB)
  • Unicode CJK Unified Ideographs Extension B (PDF, 13 MB)
• GB18030 Support Package for Windows 2000/XP, including Chinese, Tibetan, Yi, Mongolian and Thai font by Microsoft (Internet Archive)
• SIL's freeware fonts, editors and documentation

• Guobiao standards
• Unicode Transformation Formats
• Chinese character encodings

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