CS253

CS253: Software Development with C++

Spring 2018

Unicode

See this page as a slide show

Unicode

Unicode (ISO-10646)

U+ notation

By convention, Unicode code points are represented as U+ followed by at four (more only if needed) upper-case hexadecimal digits.

U+005D]RIGHT SQUARE BRACKET
U+00F1ñLATIN SMALL LETTER N WITH TILDE
U+042FЯCYRILLIC CAPITAL LETTER YA
U+2622☢RADIOACTIVE SIGN
U+1F3A9🎩TOP HAT

RIGHT SQUARE BRACKET is written U+005D, not U+5D. You could also call it Unicode character #93, but don’t.

What’s in Unicode

ASCII: A-ZDingbats: ✈ ☞ ✌ ✔ ✰ ☺ ♥ ♦ ♣ ♠ •
Other Latin: ä ñ « »Emoji: 🐱
Cyrillic: ЯEgyptian hieroglyphics: 𓁥
Hebrew: אMathematics: ∃ 𝒋 : 𝒋 ∉ ℝ
Chinese: ⿂Musical notation: 𝄞 𝄵 𝆖 𝅘𝅥𝅮
Japanese: アno Klingon ☹

All Unicode “blocks”: http://unicode.org/Public/UNIDATA/Blocks.txt

Code Points

Initially, Unicode is all about mapping integers to characters:

DecimalU+hexMeaningExample
97U+0061LATIN SMALL LETTER Aa
9786U+263AWHITE SMILING FACE☺
66506U+103CAOLD PERSIAN SIGN AURAMAZDAAHA𐏊

Now, do that for 128,000+ more characters.

Encoding

Fine, so we’ve defined this mapping. How do we actually represent those in a computer? That’s the job of an encoding. An encoding is a mapping of the bits in an integer to bytes.

16-bit Encodings


 ····J···· ····a···· ····c···· ····k····
┌────┬────┬────┬────┬────┬────┬────┬────┐
│ 00 │ 4A │ 00 │ 61 │ 00 │ 63 │ 00 │ 6B │
└────┴────┴────┴────┴────┴────┴────┴────┘
  0    1    2    3    4    5    6    7

16-bit Encodings

UTF-16:

32-bit Encodings

UTF-32:


  ········J········   ········a········   ········c········   ········k········
┌────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┬────┐
│ 00 │ 00 │ 00 │ 4A │ 00 │ 00 │ 00 │ 61 │ 00 │ 00 │ 00 │ 63 │ 00 │ 00 │ 00 │ 6B │
└────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┴────┘
   0    1    2    3    4    5    6    7    8    9   10   11   12   13   14   15

False Positives

Hey, there’s a slash in this string! No, wait, there isn’t.

When using UTF-16 or UTF-32 encoding, a naïve algorithm will falsely detect a slash (oh, excuse me, a solidus) in one of the bytes of U+262F.

Similarly, a C-string cannot hold a UTF-16 or UTF-32 string, because of the embedded zero bytes.

UTF-8 Variable-Length Encoding

BitsRangeByte 1Byte 2Byte 3Byte 4
7U+0000–U+007F0xxxxxxx 
11U+0080–U+07FF110xxxxx10xxxxxx 
16U+0800–U+FFFF1110xxxx10xxxxxx10xxxxxx 
21U+10000–U+1FFFFF11110xxx10xxxxxx10xxxxxx10xxxxxx
  J    a    c    k
┌────┬────┬────┬────┐
│ 4A │ 61 │ 63 │ 6B │
└────┴────┴────┴────┘
  0    1    2    3

Illustration of Various Encodings

U+CharDescriptionUTF-32BEUTF-16BEUTF-8
U+0041AA00000041004141
U+03A9ΩOmega000003A903A9CE A9
U+4DCA䷊Hexagram for peace00004DCA4DCAE4 B7 8A
U+1F42E🐮Mooooooooo!0001F42ED83D DC2EF0 9F 90 AE

Example

BitsRangeByte 1Byte 2Byte 3Byte 4
7U+0000–U+007F0xxxxxxx 
11U+0080–U+07FF110xxxxx10xxxxxx 
16U+0800–U+FFFF1110xxxx10xxxxxx10xxxxxx 
21U+10000–U+1FFFFF11110xxx10xxxxxx10xxxxxx10xxxxxx
  • Consider U+1F42E 🐮
    • 1F42E16 = 1 1111 0100 0010 11102 (17 bits)
    • Need 21 bits, add leading zeroes: 0 0001 1111 0100 0010 1110
    • Grouped properly: 000 011111 010000 101110
    • Byte #1: 11110xxx, use first three bits, 11110 000
    • Byte #2: 10xxxxxx, use the next six bits, 10 011111
    • Byte #3: 10xxxxxx, use the next six bits, 10 010000
    • Byte #4: 10xxxxxx, use the next six bits, 10 101110
    • All the bits:
      • 11110 000  10 011111  10 010000  10 101110
      • 11110000   10011111   10010000   10101110
      • 1111 0000  1001 1111  1001 0000  1010 1110
      • F0 9F 90 AE

Byte Order Mark

Often, files contain a “magic number”—initial bytes that indicate what sort of file it is.

EncodingBytes
UTF-32BE00 00 FE FF
UTF-32LEFF FE 00 00
UTF-16BEFE FF
UTF-16LEFF FE
UTF-8EF BB BF

The character U+FEFF ZERO WIDTH NO BREAK SPACE, is also used as a Byte Order Mark, or BOM. When used as the first bytes of a data file, indicates the encoding (assuming that you’re limited to Unicode).

If not processed as a BOM, then ZERO WIDTH NO BREAK SPACE is mostly harmless.

Programming

It’s all about bytes vs. characters. Too many languages have no byte type, so programmers use char instead. Trouble! The language has no idea whether you’re processing text, which should be treated as Unicode, or bytes of data, which would happen if a program were parsing a JPEG file.

Linux Commands

echo \u: up to four digits; \U: up to eight digits

    % echo -e '\uf1'
    ñ
    % echo -e '\U1f435'
    🐵

wc -c counts bytes; wc -m counts characters

    % echo -e '\U1f435' | wc -c
    5
    % echo -e '\U1f435' | wc -m
    2

Viewing Files

View with xxd or od:

    % echo -e 'ABC' | xxd
    00000000: 4142 430a                                ABC.
    % echo -e '\U1f435' | xxd
    00000000: f09f 90b5 0a                             .....

    % echo -e 'ABC' | od -t x1
    0000000 41 42 43 0a
    0000004
    % echo -e '\U1f435' | od -t x1
    0000000 f0 9f 90 b5 0a
    0000005

Modified: 2017-05-09T21:29

User: Guest

Check: HTML CSS
Edit History Source
Apply to CSU | Contact CSU | Disclaimer | Equal Opportunity
Colorado State University, Fort Collins, CO 80523 USA
© 2015 Colorado State University
CS Building