I have few questions about UTF-8
Is it possible to encode any Unicode with UTF-8 ?
Does utf-8 allow to encode any ascii character using only 1 byte ?
Is length of UTF-8 encoding fixed ?
My answers to check :
1) No, it's not possible. It is possible to encode 1,112,064 out of 1,114,112 codes
2) Yes
3) No, it could be 1,2,3 or 4 bytes
For question (1), what do you mean by "any Unicode"?
Do you mean "Any valid unicode character"? Then yes.
Do you mean "any possible character value from 0x0 to 0x10FFFF, including the 2048 surrogate code points that are not valid unicode character values?" Then no, but only because a valid UTF-8 decoder should reject those values.
The scheme defined by UTF-8 is perfectly capable of encoding those surrogate values in isolation, and in fact it's simpler to write UTF-8 encoding/decoding software that just handles those values like any other.
Related
I have a character appearing over the wire that has a hex value and octal value \xb1 and \261.
This is what my header looks like:
From: "\261Central Station <sip#...>"
Looking at the ASCII table the character in the picture is "±":
What I don't understand:
If I try to test the same by passing "±Central Station" in the header I see it converted to "\xC2\xB1". Why?
How can I have "\xB1" or "\261" appearing over the wire instead of "\xC2\xB1".
e. If I try to print "\xB1" or "\261" I never see "±" being printed. But if I print "\u00b1" it prints the desired character, I'm assuming because "\u00b1" is the Unicode format.
From the page you linked to:
The extended ASCII codes (character code 128-255)
There are several different variations of the 8-bit ASCII table. The table below is according to ISO 8859-1, also called ISO Latin-1.
That's worth reading twice. The character codes 128–255 aren't ASCII (ASCII is a 7-bit encoding and ends at 127).
Assuming that you're correct that the character in question is ± (it's likely, but not guaranteed), your text could be encoded ISO 8850-1 or, as #muistooshort kindly pointed out in the comments, any of a number of other ISO 8859-X or CP-12XX (Windows-12XX) encodings. We do know, however, that the text isn't (valid) UTF-8, because 0xb1 on its own isn't a valid UTF-8 character.
If you're lucky, whatever client is sending this text specified the encoding in the Content-Type header.
As to your questions:
If I try to test the same by passing ±Central Station in header I see it get converted to \xC2\xB1. Why?
The text you're passing is in UTF-8, and the bytes that represent ± in UTF-8 are 0xC2 0xB1.
How can I have \xB1 or \261 appearing over the wire instead of \xC2\xB1?
We have no idea how you're testing this, so we can't answer this question. In general, though: Either send the text encoded as ISO 8859-1 (Encoding::ISO_8859_1 in Ruby), or whatever encoding the original text was in, or as raw bytes (Encoding::ASCII_8BIT or Encoding::BINARY, which are aliases for each other).
If I try to print \xB1 or \261 I never see ± being printed. But if I print \u00b1 it prints the desired character. (I'm assuming because \u00b1 is the unicode format but I will love If some can explain this in detail.)
That's not a question, but the reason is that \xB1 (\261) is not a valid UTF-8 character. Some interfaces will print � for invalid characters; others will simply elide them. \u00b1, on the other hand, is a valid Unicode code point, which Ruby knows how to represent in UTF-8.
Brief aside: UTF-8 (like UTF-16 and UTF-32) is a character encoding specified by the Unicode standard. U+00B1 is the Unicode code point for ±, and 0xC2 0xB1 are the bytes that represent that code point in UTF-8. In Ruby we can represent UTF-8 characters using either the Unicode code point (\u00b1) or the UTF-8 bytes (in hex: \xC2\xB1; or octal: \302\261, although I don't recommend the latter since fewer Rubyists are familiar with it).
Character encoding is a big topic, well beyond the scope of a Stack Overflow answer. For a good primer, read Joel Spolsky's "The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)", and for more details on how character encoding works in Ruby read Yehuda Katz's "Encodings, Unabridged". Reading both will take you less than 30 minutes and will save you hundreds of hours of pain in the future.
I would like to know if :
all characters encoded in ANSI (1252) could be converted to UTF-8 without any problem.
all characters encoded in UTF-8 couldn't be converted to ANSI (1252) without any problem (example : Ǣ couldn't be converted to ANSI encoding).
Could you confirm for me that it corrects ?
Thanks !
Yes, all characters representable in Windows-1252 have Unicode equivalents, and can therefore be converted to UTF-8. See this Wikipedia article for a table showing the mapping to Unicode code points.
And since Windows-1252 is an 8-bit character set, and UTF-8 can represent many thousands of distinct characters, there are obviously plenty of characters representable as UTF-8 and not representable as Windows-1252.
Note that the name "ANSI" for the Windows-1252 encoding is strictly incorrect. When it was first proposed, it was intended to be an ANSI standard, but that never happened. Unfortunately, the name stuck. (Microsoft-related documentation also commonly refers to UTF-16 as "Unicode", another misnomer; UTF-16 is one representation of Unicode, but there are others.)
As far as I know - base 64 can represent any char. ( inclduing binary)
Base64 encoding schemes are commonly used when there is a need to
encode binary(!) data that need to be stored and transferred over
media that are designed to deal with textual data
So I tried to apply it on extended ascii char ( beyond the 127)
the char :
after following the simple algorithm :
I got to :
so the value should be Fy
So why when I use online-encoder and put the value by alt+178 ,
I get this result :
What is going on here ?
Your browser sent the encoding website the UTF-8 encoding of the character. This encoding is not 178.
That is the UTF-8 encoding of unicode character U+2593, which is the same as extended ASCII character 178.
Thanks to Damien_The_Unbeliever && zmbq &&Markus Jarderot :
so
I have these values from a unicode database but I'm not sure how to translate them into the human readable form. What are these even called?
Here they are:
U+2B71F
U+2A52D
U+2A68F
U+2A690
U+2B72F
U+2B4F7
U+2B72B
How can I convert these to there readable symbols?
How about:
# Using pack
puts ["2B71F".hex].pack("U")
# Using chr
puts (0x2B71F).chr(Encoding::UTF_8)
In Ruby 1.9+ you can also do:
puts "\u{2B71F}"
I.e. the \u{} escape sequence can be used to decode Unicode codepoints.
The unicode symbols like U+2B71F are referred to as a codepoint.
The unicode system defines a unique codepoint for each character in a multitude of world languages, scientific symbols, currencies etc. This character set is steadily growing.
For example, U+221E is infinity.
The codepoints are hexadecimal numbers. There is always exactly one number defined per character.
There are many ways to arrange this in memory. This is known as an encoding of which the common ones are UTF-8 and UTF-16. The conversion to and fro is well defined.
Here you are most probably looking for converting the unicode codepoint to UTF-8 characters.
codepoint = "U+2B71F"
You need to extract the hex part coming after U+ and get only 2B71F. This will be the first group capture. See this.
codepoint.to_s =~ /U\+([0-9a-fA-F]{4,5}|10[0-9a-fA-F]{4})$/
And you're UTF-8 character will be:
utf_8_character = [$1.hex].pack("U")
References:
Convert Unicode codepoints to UTF-8 characters with Module#const_missing.
Tim Bray on the goodness of unicode.
Joel Spolsky - The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!).
Dissecting the Unicode regular expression
I have a procedure that imports a binary file containing some strings. The strings can contain extended ASCII, e.g. CHR(224), 'à'. The procedure is taking a RAW and converting the BCD bytes into characters in a string one by one.
The problem is that the extended ASCII characters are getting lost. I suspect this is due to their values meaning something else in UTF8.
I think what I need is a function that takes an ASCII character index and returns the appropriate UTF8 character.
Update: If I happen to know the equivalent Oracle character set for the incoming text can I then convert the raw bytes to UTF8? The source text will always be single byte.
There's no such thing as "extended ASCII." Or, to be more precise, so many encodings are supersets of ASCII, sharing the same first 127 code points, that the term is too vague to be meaningful. You need to find out if the strings in this file are encoded using UTF-8, ISO-8859-whatever, MacRoman, etc.
The answer to the second part of your question is the same. UTF-8 is, by design, a superset of ASCII. Any ASCII character (i.e. 0 through 127) is also a UTF-8 character. To translate some non-ASCII character (i.e. >= 128) into UTF-8, you first need to find out what encoding it's in.