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GB18030 is the registered Internet name for the official character set of the People's Republic of China (PRC) superseding GB2312. This character set is formally called "Chinese National Standard GB 18030-2000: Information Technology -- Chinese ideograms coded character set for information interchange -- Extension for the basic set". GB abbreviates Guójiā Biāozhǔn (国家标准), which means national standard in Chinese. The standard was published by the China Standard Press, Beijing, March 17, 2000 and updated November 20, 2000. As of August 1, 2006, support for this character set is officially mandatory for all software products sold in the PRC. Due to its Unicode equivalence, GB18030 supports both simplified and traditional Chinese characters.

GB18030 can be considered a Unicode Transformation Format (i.e. an encoding of all Unicode code points) that maintains compatibility with a legacy character set. In other words, it is a Chinese equivalent of UTF-8 (which maintains compatibility with ASCII). Like UTF-8, GB18030 is a superset of ASCII and can represent the whole range of Unicode code points; in addition, it is also a superset of GB2312. GB18030 also maintains compatibility with GBK, Microsoft's extended version of GB2312, with the exception of the euro sign which is given a single byte code of 0x80 in Microsoft's later versions of GBK and a two byte code of A2 E3 in GB18030.

Part of the mapping data is from a lookup table (similarly to GBK). The rest is calculated algorithmically. Unfortunately it also inherits the bad aspects of the legacy standards it's based on (most notably needing special code to safely find ASCII characters in a GB18030 sequence).

Most major computer companies had already standardised on some version of Unicode as the primary format for use in their binary formats and OS calls. However, they mostly had only supported code points in the BMP originally defined in Unicode 1.0, which supported only 65,536 codepoints and was often encoded in 16 bits as UCS-2.

In a move of historic significance for software supporting Unicode, the PRC decided to mandate support of certain code points outside the BMP. This means that software can no longer get away with treating characters as 16 bit fixed width entities (UCS-2). Therefore they must either process the data in a variable width format (such as UTF-8 or UTF-16), which are the most common choices, or move to a larger fixed width format (such as UCS-4 or UTF-32). Microsoft made the change from UCS-2 to UTF-16 with Windows 2000.

Windows 2000 can support the GB18030 encoding if GB18030 Support Package [1] is installed. Windows XP can support it natively.

More specifically, supporting the GB18030 encoding on Windows means that Code Page 54936 is supported by MultiByteToWideChar and WideCharToMultiByte. 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 when the file in question does not contain any character that does not exist in the Code Page 936, including most characters belonging to non-Chinese scripts (see below for examples).

GB18030 Support Package contains SimSun18030.ttc, a TrueType font collection file which combines two Chinese fonts, SimSun-18030 and NSimSun-18030.

The SimSun 18030 font includes all the characters in Unicode 2.1 plus new characters found in the Unicode CJK Unified Ideographs Extension A section, but despite its name, it does not contain glyphs for all GB 18030 characters. Note that all (about a million) Unicode code points up to U+10FFFF can be encoded as GB 18030, hence “a font that fully supports GB 18030” would mean a font that contains glyphs for all Unicode characters, not only for CJK ones. HAN NOM A and HAN NOM B [2] are free fonts, which include all the characters in the Extension A and the Extension B, more exhaustive than SimSun-18030, or even than Simsun (Founder Extended), but they don't support all code points defined in Unicode 5.0.0 either.

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 (the ASCII 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 safe for GB18030 (in much the same way that a basic byte-oriented search routine is reasonably safe for EUC).

This gives a total of 1,587,600 (126*10*126*10) possible 4 byte sequences, which is easily sufficient to cover Unicode's 1,112,046 (17 × 65536 - 2048 surrogates - 18 noncharacters) code points.

Unfortunately, to further complicate matters there are no simple rules to translate between a 4 byte sequence and its corresponding code 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. For example:

U+00DE (Þ) → 81 30 89 37
U+00DF (ß) → 81 30 89 38
U+00E0 (à) → A8 A4
U+00E1 (á) → A8 A2
U+00E2 (â) → 81 30 89 39
U+00E3 (ã) → 81 30 8A 30

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

• IANA Charset Registration for GB18030
• English language summary of GB 18030-2000
• Introduction to GB18030 including evolution from GB2312 and GBK (Sun)
• GB18030: A mega-codepage (IBM DeveloperWorks)
• A Look at China’s New GB 18030 Character Set Standard
• Authoritative mapping table between GB18030 and Unicode Due to a bug in Firefox, this large XML file may cause Firefox to hang. Other browsers can handle this file.
• ICU Converter Explorer: GB18030
• Unicode CJK Unified Ideographs Extension A (PDF, 1.5MB)
• 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
• SIL's freeware fonts, editors and documentation