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Halfwidth and fullwidth forms

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Subject: Numerals in Unicode, Unicode, Unicode character property, Plane (Unicode), Reference desk/Archives/Computing/2010 August 22
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Halfwidth and fullwidth forms

A Korean command prompt (cmd.exe) showing halfwidth and fullwidth characters.

In CJK (Chinese, Japanese and Korean) computing, graphic characters are traditionally classed into fullwidth (in Taiwan and Hong Kong: 全形; in CJK and Japanese: 全角) and halfwidth (in Taiwan and Hong Kong: 半形; in CJK and Japanese: 半角) characters. With fixed-width fonts, a halfwidth character occupies half the width of a fullwidth character, hence the name.

In the days of computer terminals and text mode computing, characters were normally laid out in a grid, often 80 columns by 24 or 25 lines. Each character was displayed as a small dot matrix, often about 8 pixels wide, and an SBCS (single byte character set) was generally used to encode characters of western languages.

For a number of practical and aesthetic reasons, Han characters would need to be twice as wide as these fixed-width SBCS characters. These "fullwidth characters" were typically encoded in a DBCS (double byte character set), although less common systems used other variable-width character sets that used more bytes per character.

Halfwidth and Fullwidth Forms is also the name of a Unicode block U+FF00–FFEF.

In Unicode

In Unicode, if a certain grapheme can be represented as either a fullwidth character or a halfwidth character, it is said to have both a fullwidth form and a halfwidth form.

Halfwidth and Fullwidth Forms is the name of Unicode block U+FF00–FFEF, the last of the Basic Multilingual Plane excepting the short Specials block at U+FFF0–FFFF.

Range U+FF01–FF5E reproduces the characters of ASCII 21 to 7E as fullwidth forms, that is, a fixed width form used in CJK computing. This is useful for typesetting Latin characters in a CJK environment. U+FF00 does not correspond to a fullwidth ASCII 20 (space character), since that role is already fulfilled by U+3000 "ideographic space."

Range U+FF65–FFDC encodes halfwidth forms of Katakana and Hangul characters – see half-width kana. Range U+FFE0–FFEE includes fullwidth and halfwidth symbols.

Chart

Halfwidth and Fullwidth Forms[1][2]
Official Unicode Consortium code chart (PDF)
  0 1 2 3 4 5 6 7 8 9 A B C D E F
U+FF0x
U+FF1x
U+FF2x
U+FF3x _
U+FF4x
U+FF5x
U+FF6x
U+FF7x ソ
U+FF8x
U+FF9x
U+FFAx  HW 
HF
U+FFBx
U+FFCx
U+FFDx
U+FFEx
Notes
1.^ As of Unicode version 7.0
2.^ Grey areas indicate non-assigned code points

See also

External links

  • Halfwidth and Fullwidth Forms at Alan Wood's Unicode Resources
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