What's different between UTF-8 and UTF-8 with BOM? Which is better?
The UTF-8 BOM is a sequence of bytes at the start of a text stream (0xEF, 0xBB, 0xBF) that allows the reader to more reliably guess a file as being encoded in UTF-8.
Normally, the BOM is used to signal the endianness of an encoding, but since endianness is irrelevant to UTF-8, the BOM is unnecessary.
According to the Unicode standard, the BOM for UTF-8 files is not recommended:
2.6 Encoding Schemes
... Use of a BOM is neither required nor recommended for UTF-8, but may be encountered in contexts where UTF-8 data is converted from other encoding forms that use a BOM or where the BOM is used as a UTF-8 signature. See the “Byte Order Mark” subsection in Section 16.8, Specials, for more information.
The other excellent answers already answered that:
There is no official difference between UTF-8 and BOM-ed UTF-8
A BOM-ed UTF-8 string will start with the three following bytes. EF BB BF
Those bytes, if present, must be ignored when extracting the string from the file/stream.
But, as additional information to this, the BOM for UTF-8 could be a good way to "smell" if a string was encoded in UTF-8... Or it could be a legitimate string in any other encoding...
For example, the data [EF BB BF 41 42 43] could either be:
The legitimate ISO-8859-1 string "ABC"
The legitimate UTF-8 string "ABC"
So while it can be cool to recognize the encoding of a file content by looking at the first bytes, you should not rely on this, as show by the example above
Encodings should be known, not divined.
There are at least three problems with putting a BOM in UTF-8 encoded files.
Files that hold no text are no longer empty because they always contain the BOM.
Files that hold text within the ASCII subset of UTF-8 are no longer themselves ASCII because the BOM is not ASCII, which makes some existing tools break down, and it can be impossible for users to replace such legacy tools.
It is not possible to concatenate several files together because each file now has a BOM at the beginning.
And, as others have mentioned, it is neither sufficient nor necessary to have a BOM to detect that something is UTF-8:
It is not sufficient because an arbitrary byte sequence can happen to start with the exact sequence that constitutes the BOM.
It is not necessary because you can just read the bytes as if they were UTF-8; if that succeeds, it is, by definition, valid UTF-8.
Here are examples of the BOM usage that actually cause real problems and yet many people don't know about it.
BOM breaks scripts
Shell scripts, Perl scripts, Python scripts, Ruby scripts, Node.js scripts or any other executable that needs to be run by an interpreter - all start with a shebang line which looks like one of those:
#!/bin/sh
#!/usr/bin/python
#!/usr/local/bin/perl
#!/usr/bin/env node
It tells the system which interpreter needs to be run when invoking such a script. If the script is encoded in UTF-8, one may be tempted to include a BOM at the beginning. But actually the "#!" characters are not just characters. They are in fact a magic number that happens to be composed out of two ASCII characters. If you put something (like a BOM) before those characters, then the file will look like it had a different magic number and that can lead to problems.
See Wikipedia, article: Shebang, section: Magic number:
The shebang characters are represented by the same two bytes in
extended ASCII encodings, including UTF-8, which is commonly used for
scripts and other text files on current Unix-like systems. However,
UTF-8 files may begin with the optional byte order mark (BOM); if the
"exec" function specifically detects the bytes 0x23 and 0x21, then the
presence of the BOM (0xEF 0xBB 0xBF) before the shebang will prevent
the script interpreter from being executed. Some authorities recommend
against using the byte order mark in POSIX (Unix-like) scripts,[14]
for this reason and for wider interoperability and philosophical
concerns. Additionally, a byte order mark is not necessary in UTF-8,
as that encoding does not have endianness issues; it serves only to
identify the encoding as UTF-8. [emphasis added]
BOM is illegal in JSON
See RFC 7159, Section 8.1:
Implementations MUST NOT add a byte order mark to the beginning of a JSON text.
BOM is redundant in JSON
Not only it is illegal in JSON, it is also not needed to determine the character encoding because there are more reliable ways to unambiguously determine both the character encoding and endianness used in any JSON stream (see this answer for details).
BOM breaks JSON parsers
Not only it is illegal in JSON and not needed, it actually breaks all software that determine the encoding using the method presented in RFC 4627:
Determining the encoding and endianness of JSON, examining the first four bytes for the NUL byte:
00 00 00 xx - UTF-32BE
00 xx 00 xx - UTF-16BE
xx 00 00 00 - UTF-32LE
xx 00 xx 00 - UTF-16LE
xx xx xx xx - UTF-8
Now, if the file starts with BOM it will look like this:
00 00 FE FF - UTF-32BE
FE FF 00 xx - UTF-16BE
FF FE 00 00 - UTF-32LE
FF FE xx 00 - UTF-16LE
EF BB BF xx - UTF-8
Note that:
UTF-32BE doesn't start with three NULs, so it won't be recognized
UTF-32LE the first byte is not followed by three NULs, so it won't be recognized
UTF-16BE has only one NUL in the first four bytes, so it won't be recognized
UTF-16LE has only one NUL in the first four bytes, so it won't be recognized
Depending on the implementation, all of those may be interpreted incorrectly as UTF-8 and then misinterpreted or rejected as invalid UTF-8, or not recognized at all.
Additionally, if the implementation tests for valid JSON as I recommend, it will reject even the input that is indeed encoded as UTF-8, because it doesn't start with an ASCII character < 128 as it should according to the RFC.
Other data formats
BOM in JSON is not needed, is illegal and breaks software that works correctly according to the RFC. It should be a nobrainer to just not use it then and yet, there are always people who insist on breaking JSON by using BOMs, comments, different quoting rules or different data types. Of course anyone is free to use things like BOMs or anything else if you need it - just don't call it JSON then.
For other data formats than JSON, take a look at how it really looks like. If the only encodings are UTF-* and the first character must be an ASCII character lower than 128 then you already have all the information needed to determine both the encoding and the endianness of your data. Adding BOMs even as an optional feature would only make it more complicated and error prone.
Other uses of BOM
As for the uses outside of JSON or scripts, I think there are already very good answers here. I wanted to add more detailed info specifically about scripting and serialization, because it is an example of BOM characters causing real problems.
What's different between UTF-8 and UTF-8 without BOM?
Short answer: In UTF-8, a BOM is encoded as the bytes EF BB BF at the beginning of the file.
Long answer:
Originally, it was expected that Unicode would be encoded in UTF-16/UCS-2. The BOM was designed for this encoding form. When you have 2-byte code units, it's necessary to indicate which order those two bytes are in, and a common convention for doing this is to include the character U+FEFF as a "Byte Order Mark" at the beginning of the data. The character U+FFFE is permanently unassigned so that its presence can be used to detect the wrong byte order.
UTF-8 has the same byte order regardless of platform endianness, so a byte order mark isn't needed. However, it may occur (as the byte sequence EF BB FF) in data that was converted to UTF-8 from UTF-16, or as a "signature" to indicate that the data is UTF-8.
Which is better?
Without. As Martin Cote answered, the Unicode standard does not recommend it. It causes problems with non-BOM-aware software.
A better way to detect whether a file is UTF-8 is to perform a validity check. UTF-8 has strict rules about what byte sequences are valid, so the probability of a false positive is negligible. If a byte sequence looks like UTF-8, it probably is.
UTF-8 with BOM is better identified. I have reached this conclusion the hard way. I am working on a project where one of the results is a CSV file, including Unicode characters.
If the CSV file is saved without a BOM, Excel thinks it's ANSI and shows gibberish. Once you add "EF BB BF" at the front (for example, by re-saving it using Notepad with UTF-8; or Notepad++ with UTF-8 with BOM), Excel opens it fine.
Prepending the BOM character to Unicode text files is recommended by RFC 3629: "UTF-8, a transformation format of ISO 10646", November 2003
at https://www.rfc-editor.org/rfc/rfc3629 (this last info found at: http://www.herongyang.com/Unicode/Notepad-Byte-Order-Mark-BOM-FEFF-EFBBBF.html)
BOM tends to boom (no pun intended (sic)) somewhere, someplace. And when it booms (for example, doesn't get recognized by browsers, editors, etc.), it shows up as the weird characters  at the start of the document (for example, HTML file, JSON response, RSS, etc.) and causes the kind of embarrassments like the recent encoding issue experienced during the talk of Obama on Twitter.
It's very annoying when it shows up at places hard to debug or when testing is neglected. So it's best to avoid it unless you must use it.
Question: What's different between UTF-8 and UTF-8 without a BOM? Which is better?
Here are some excerpts from the Wikipedia article on the byte order mark (BOM) that I believe offer a solid answer to this question.
On the meaning of the BOM and UTF-8:
The Unicode Standard permits the BOM in UTF-8, but does not require
or recommend its use. Byte order has no meaning in UTF-8, so its
only use in UTF-8 is to signal at the start that the text stream is
encoded in UTF-8.
Argument for NOT using a BOM:
The primary motivation for not using a BOM is backwards-compatibility
with software that is not Unicode-aware... Another motivation for not
using a BOM is to encourage UTF-8 as the "default" encoding.
Argument FOR using a BOM:
The argument for using a BOM is that without it, heuristic analysis is
required to determine what character encoding a file is using.
Historically such analysis, to distinguish various 8-bit encodings, is
complicated, error-prone, and sometimes slow. A number of libraries
are available to ease the task, such as Mozilla Universal Charset
Detector and International Components for Unicode.
Programmers mistakenly assume that detection of UTF-8 is equally
difficult (it is not because of the vast majority of byte sequences
are invalid UTF-8, while the encodings these libraries are trying to
distinguish allow all possible byte sequences). Therefore not all
Unicode-aware programs perform such an analysis and instead rely on
the BOM.
In particular, Microsoft compilers and interpreters, and many
pieces of software on Microsoft Windows such as Notepad will not
correctly read UTF-8 text unless it has only ASCII characters or it
starts with the BOM, and will add a BOM to the start when saving text
as UTF-8. Google Docs will add a BOM when a Microsoft Word document is
downloaded as a plain text file.
On which is better, WITH or WITHOUT the BOM:
The IETF recommends that if a protocol either (a) always uses UTF-8,
or (b) has some other way to indicate what encoding is being used,
then it “SHOULD forbid use of U+FEFF as a signature.”
My Conclusion:
Use the BOM only if compatibility with a software application is absolutely essential.
Also note that while the referenced Wikipedia article indicates that many Microsoft applications rely on the BOM to correctly detect UTF-8, this is not the case for all Microsoft applications. For example, as pointed out by #barlop, when using the Windows Command Prompt with UTF-8†, commands such type and more do not expect the BOM to be present. If the BOM is present, it can be problematic as it is for other applications.
† The chcp command offers support for UTF-8 (without the BOM) via code page 65001.
This question already has a million-and-one answers and many of them are quite good, but I wanted to try and clarify when a BOM should or should not be used.
As mentioned, any use of the UTF BOM (Byte Order Mark) in determining whether a string is UTF-8 or not is educated guesswork. If there is proper metadata available (like charset="utf-8"), then you already know what you're supposed to be using, but otherwise you'll need to test and make some assumptions. This involves checking whether the file a string comes from begins with the hexadecimal byte code, EF BB BF.
If a byte code corresponding to the UTF-8 BOM is found, the probability is high enough to assume it's UTF-8 and you can go from there. When forced to make this guess, however, additional error checking while reading would still be a good idea in case something comes up garbled. You should only assume a BOM is not UTF-8 (i.e. latin-1 or ANSI) if the input definitely shouldn't be UTF-8 based on its source. If there is no BOM, however, you can simply determine whether it's supposed to be UTF-8 by validating against the encoding.
Why is a BOM not recommended?
Non-Unicode-aware or poorly compliant software may assume it's latin-1 or ANSI and won't strip the BOM from the string, which can obviously cause issues.
It's not really needed (just check if the contents are compliant and always use UTF-8 as the fallback when no compliant encoding can be found)
When should you encode with a BOM?
If you're unable to record the metadata in any other way (through a charset tag or file system meta), and the programs being used like BOMs, you should encode with a BOM. This is especially true on Windows where anything without a BOM is generally assumed to be using a legacy code page. The BOM tells programs like Office that, yes, the text in this file is Unicode; here's the encoding used.
When it comes down to it, the only files I ever really have problems with are CSV. Depending on the program, it either must, or must not have a BOM. For example, if you're using Excel 2007+ on Windows, it must be encoded with a BOM if you want to open it smoothly and not have to resort to importing the data.
UTF-8 without BOM has no BOM, which doesn't make it any better than UTF-8 with BOM, except when the consumer of the file needs to know (or would benefit from knowing) whether the file is UTF-8-encoded or not.
The BOM is usually useful to determine the endianness of the encoding, which is not required for most use cases.
Also, the BOM can be unnecessary noise/pain for those consumers that don't know or care about it, and can result in user confusion.
It should be noted that for some files you must not have the BOM even on Windows. Examples are SQL*plus or VBScript files. In case such files contains a BOM you get an error when you try to execute them.
Quoted at the bottom of the Wikipedia page on BOM: http://en.wikipedia.org/wiki/Byte-order_mark#cite_note-2
"Use of a BOM is neither required nor recommended for UTF-8, but may be encountered in contexts where UTF-8 data is converted from other encoding forms that use a BOM or where the BOM is used as a UTF-8 signature"
UTF-8 with BOM only helps if the file actually contains some non-ASCII characters. If it is included and there aren't any, then it will possibly break older applications that would have otherwise interpreted the file as plain ASCII. These applications will definitely fail when they come across a non ASCII character, so in my opinion the BOM should only be added when the file can, and should, no longer be interpreted as plain ASCII.
I want to make it clear that I prefer to not have the BOM at all. Add it in if some old rubbish breaks without it, and replacing that legacy application is not feasible.
Don't make anything expect a BOM for UTF-8.
I look at this from a different perspective. I think UTF-8 with BOM is better as it provides more information about the file. I use UTF-8 without BOM only if I face problems.
I am using multiple languages (even Cyrillic) on my pages for a long time and when the files are saved without BOM and I re-open them for editing with an editor (as cherouvim also noted), some characters are corrupted.
Note that Windows' classic Notepad automatically saves files with a BOM when you try to save a newly created file with UTF-8 encoding.
I personally save server side scripting files (.asp, .ini, .aspx) with BOM and .html files without BOM.
When you want to display information encoded in UTF-8 you may not face problems. Declare for example an HTML document as UTF-8 and you will have everything displayed in your browser that is contained in the body of the document.
But this is not the case when we have text, CSV and XML files, either on Windows or Linux.
For example, a text file in Windows or Linux, one of the easiest things imaginable, it is not (usually) UTF-8.
Save it as XML and declare it as UTF-8:
<?xml version="1.0" encoding="UTF-8"?>
It will not display (it will not be be read) correctly, even if it's declared as UTF-8.
I had a string of data containing French letters, that needed to be saved as XML for syndication. Without creating a UTF-8 file from the very beginning (changing options in IDE and "Create New File") or adding the BOM at the beginning of the file
$file="\xEF\xBB\xBF".$string;
I was not able to save the French letters in an XML file.
One practical difference is that if you write a shell script for Mac OS X and save it as plain UTF-8, you will get the response:
#!/bin/bash: No such file or directory
in response to the shebang line specifying which shell you wish to use:
#!/bin/bash
If you save as UTF-8, no BOM (say in BBEdit) all will be well.
The Unicode Byte Order Mark (BOM) FAQ provides a concise answer:
Q: How I should deal with BOMs?
A: Here are some guidelines to follow:
A particular protocol (e.g. Microsoft conventions for .txt files) may require use of the BOM on certain Unicode data streams, such as
files. When you need to conform to such a protocol, use a BOM.
Some protocols allow optional BOMs in the case of untagged text. In those cases,
Where a text data stream is known to be plain text, but of unknown encoding, BOM can be used as a signature. If there is no BOM,
the encoding could be anything.
Where a text data stream is known to be plain Unicode text (but not which endian), then BOM can be used as a signature. If there
is no BOM, the text should be interpreted as big-endian.
Some byte oriented protocols expect ASCII characters at the beginning of a file. If UTF-8 is used with these protocols, use of the
BOM as encoding form signature should be avoided.
Where the precise type of the data stream is known (e.g. Unicode big-endian or Unicode little-endian), the BOM should not be used. In
particular, whenever a data stream is declared to be UTF-16BE,
UTF-16LE, UTF-32BE or UTF-32LE a BOM must not be used.
From http://en.wikipedia.org/wiki/Byte-order_mark:
The byte order mark (BOM) is a Unicode
character used to signal the
endianness (byte order) of a text file
or stream. Its code point is U+FEFF.
BOM use is optional, and, if used,
should appear at the start of the text
stream. Beyond its specific use as a
byte-order indicator, the BOM
character may also indicate which of
the several Unicode representations
the text is encoded in.
Always using a BOM in your file will ensure that it always opens correctly in an editor which supports UTF-8 and BOM.
My real problem with the absence of BOM is the following. Suppose we've got a file which contains:
abc
Without BOM this opens as ANSI in most editors. So another user of this file opens it and appends some native characters, for example:
abg-αβγ
Oops... Now the file is still in ANSI and guess what, "αβγ" does not occupy 6 bytes, but 3. This is not UTF-8 and this causes other problems later on in the development chain.
As mentioned above, UTF-8 with BOM may cause problems with non-BOM-aware (or compatible) software. I once edited HTML files encoded as UTF-8 + BOM with the Mozilla-based KompoZer, as a client required that WYSIWYG program.
Invariably the layout would get destroyed when saving. It took my some time to fiddle my way around this. These files then worked well in Firefox, but showed a CSS quirk in Internet Explorer destroying the layout, again. After fiddling with the linked CSS files for hours to no avail I discovered that Internet Explorer didn't like the BOMfed HTML file. Never again.
Also, I just found this in Wikipedia:
The shebang characters are represented by the same two bytes in extended ASCII encodings, including UTF-8, which is commonly used for scripts and other text files on current Unix-like systems. However, UTF-8 files may begin with the optional byte order mark (BOM); if the "exec" function specifically detects the bytes 0x23 0x21, then the presence of the BOM (0xEF 0xBB 0xBF) before the shebang will prevent the script interpreter from being executed. Some authorities recommend against using the byte order mark in POSIX (Unix-like) scripts,[15] for this reason and for wider interoperability and philosophical concerns
Here is my experience with Visual Studio, Sourcetree and Bitbucket pull requests, which has been giving me some problems:
So it turns out BOM with a signature will include a red dot character on each file when reviewing a pull request (it can be quite annoying).
If you hover on it, it will show a character like "ufeff", but it turns out Sourcetree does not show these types of bytemarks, so it will most likely end up in your pull requests, which should be ok because that's how Visual Studio 2017 encodes new files now, so maybe Bitbucket should ignore this or make it show in another way, more info here:
Red dot marker BitBucket diff view
I save a autohotkey file with utf-8, the chinese characters become strang.
With utf-8 BOM, works fine.
AutoHotkey will not automatically recognize a UTF-8 file unless it begins with a byte order mark.
https://www.autohotkey.com/docs/FAQ.htm#nonascii
UTF with a BOM is better if you use UTF-8 in HTML files and if you use Serbian Cyrillic, Serbian Latin, German, Hungarian or some exotic language on the same page.
That is my opinion (30 years of computing and IT industry).
Related
I've read that adding the UTF-8 Byte Order Mark (3 characters) at the start of a text file makes it a UTF-8 file, but I've also read that unicode recommends against using the BOM for UTF-8.
I'm generating files in PHP and I have a requirement that the files be UTF-8. I've added the UTF-8 BOM to the start of the file but I've received feedback about garbage characters at the start of the file from the company that is parsing the files and that gave me the requirement to make the files UTF-8.
If I open the file in notepad it doesn't show the BOM, and if I go to save as, it shows UTF-8 as the default choice.
Opening the file in Textpad32 shows the 3 characters at the start of the file.
So what makes a file UTF-8?
Text is UTF-8 because it's valid as UTF-8 and the author decides it is.
How that decision by the author is communicated to the consumer is a different question, which involves convention, guessing, and various schemes for in-band- or out-of-band-signalling, like HTTP or HTML charset, BOM (which enhances guessing), some envelope / embedding Format, additional data-streams, file-naming, and many more.
The file doesn't need any explicit indicator that it is UTF-8, modern text editors should detect UTF-8 encoding from the context as UTF-8 sequences are quite distinct.
Also, as you experienced for yourself, PHP doesn't like the BOM header, it's a silly thing that often messes up with the script output and creates more problems than it solves.
HTML has it's own way of declaring the encoding of a file, you can do it within the HTML itself:
<head>
<meta charset="UTF-8">
</head>
Or declare the encoding in the HTTP headers, here with PHP:
header('Content-Type: text/html; charset=utf-8');
Modern browsers will also assume UTF-8 as default encoding in case none is specified. It is the standard of the web after all.
UTF-8 is a particular encoding. All 7-bit ASCII files are also valid UTF-8, and it can encode every Unicode character as well.
You will often get the advice to save as UTF-8 without a BOM. In practice, it is very unlikely that a file in a legacy encoding (such as code page 1252, Big5 or Shift-JIS) would just happen to look like valid UTF-8 unless it is an intentionally-ambiguous test case. Many programs, such as web browsers, are good in practice at figuring out when a file is UTF-8. Most recent software uses UTF-8 as its preferred text encoding unless it’s forced to default to something else for compatibility with last century. (LaTeX, for example, changed its default source encoding to UTF-8 in April 2018, and both the LuaLaTeX and XeLaTeX engines had been doing the same for years.)
There are some document types with special requirements. For example, the default encoding of web pages is theoretically Windows 1252, although browsers in the real world will take their best guess. The current best practice on the Web is to save as UTF-8 without a BOM. Instead, you write inside the <head> of the document, <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> or <meta charset="utf-8"/> This tells the user agent explicitly what the character encoding is.
On the other hand, some older versions of software either break if they see a BOM, or only recognize UTF-8 if there is a BOM. Microsoft in the ’aughts was especially guilty of this, its software doesn’t want to break any files that used to work back then, and so, to this day, I save my C source files as UTF-8 with a BOM. This is the only format that just works on every compiler I use: even the latest version of MSVC might guess wrong if you don’t give it either a BOM or the right command-line flag, whereas Clang only supports UTF-8 and has no option to read files in any other encoding. Some older versions of MSVC that I was once forced to use cannot understand UTF-8 at all unless the BOM is there, and do not provide any way to override its autodetection.
I need to determine the character encoding of the contents of a .csv file.
Every snippet that I have seen do this uses file_get_contents(), however I can't use that because the file is too large to store in a variable (server memory limit exhausted).
How can I determine the character encoding of a file? Can I just get the first x characters and check them? Would that guarantee that my whole file is that encoding?
Alternatively, can I simply convert the entire csv to UTF-8 without knowing the current file encoding?
No, you can't determine the encoding with just the first x characters. You can guess it, and the guess may be wrong. The file may be UTF-8 but not contain UTF-8 before x characters. If may contain another encoding that is compatible with ASCII, bot only after character x.
No, you can't convert a file without knowing the current file encoding.
You can go straight to the conversion, as you said, using iconv (http://php.net/manual/en/function.iconv.php#49434)
'Pray, Mr. Babbage, if you put into the machine wrong figures, will the right answers come out?' I am not able rightly to apprehend the kind of confusion of ideas that could provoke such a question.
—Charles Babbage, 1864.
You have missing metadata and are proposing to put in values whether they are right or not.
Only the author/sender can tell you, perhaps via some standard, specification, convention, agreement or communication. A common method of communication when transferring data via HTTP is the Content-Type header.
Unfortunately, inadequate communication of metadata for text files and streams is too common in our industry. It stems from the 1970s and 80s when text files were converted to the local character encoding upon receipt. That doesn't apply anymore and nothing really took its place.
Non-answer:
Conversion from ISO-8859-1 will never fail during conversion because it uses all 256 bytes values in any sequence.
Conversion to any current Unicode encoding (including UTF-8) will never fail because all of them support the whole Unicode character set, and Unicode includes every computerized character you are likely to see today.
But wait, there is more needed metadata in the case of CSV:
line ending (arguably detectable)
field separator (arguably detectable)
quoting scheme, including escaping
presence of header row
and, finally, the datatype of each column.
And, keep in mind, if you were to guess any of this, and the data source is updatable, today's guess might not work tomorrow.
I have a fedora machine acting as server, with apache running php 5.3
A scripts acts as an entry page for various sources sending me "messages".
The php script is called like: serverAddress/phpScript.php?message=MyMessage the message is then saved via PDO to connect to SqlServer 2008 db.
If the message contains any special characters (e.g. german), like: üäöß then in the db I will get some gibberish instead of the correct string: üäöß
The db is perfectly capable of UTF-8 - I can connect and send/retrieve german characters without any issue with other tools (not via php).
Inside the php script:
if I echo the input string I get the correct string üäöß
if I save it to a file (log the input) I see the gibberish: üäöß
What is causing this behavior? How can I fix it?
multibyte is enabled (yum install php-mbstring followed by a apache restart)
at the start of my php script I have:
mb_internal_encoding('UTF-8');
mb_http_output('UTF-8');
mb_http_input('UTF-8');
mb_language('uni');
mb_regex_encoding('UTF-8');
ob_start('mb_output_handler');
from what I understand the default encoding type when dealing with mssql via PDO is UTF-8
New development:
A colleague pointed me to the PDO_DBLIB page (visible only from cache in this moment) where I saw $res->bindValue(':value', iconv('UTF-8', 'ISO8859-1', $value);
I replaced all my $res->bindParam(':text',$text); with $res->bindParam(':text',iconv('UTF-8', 'ISO8859-1',$text)); and everything worked :).
The mb_internal_encoding.... and all other lines were no longer needed.
Why does it work when using the ISO8859-1 encoding?
A database may handle special characters without even supporting the Unicode set (which UTF-8 happens to be an encoding, specifically a variable-length one).
A character set is a mapping between numbers and characters. Unicode and ASCII are common examples of charsets. Unicode states that the sign € maps to the number 8364 (really it uses the code point U+20AC). UTF-8 is a way to encode Unicode code points, and represents U+20AC with three bytes: 0xE2 0x82 0xAC; UTF-16 is another encodind for Unicode code points, which always use two bytes: 0x20AC (link). Both of these encodings refer to the same 8364th entry in the Unicode catalogue.
ASCII is both a charset and an encoding scheme: the ASCII character set maps number from 0 to 127 to 128 human chars, and the ASCII encoding requires a single byte.
Always remember that a String is a human concept. It's represented in a computer by the tuple (byte_content, encoding). Let's say you want to store Unicode strings in your database. Please, note: it's not necessary to use the Unicode set if you just need to support German users. It's useful when you want to store Arabian, Chinese, Hebrew and German at the same time in the same column. MS SQLServer uses UCS-2 to encode Unicode, and this holds true for columns declared NCHAR or NVARCHAR (note the N prefix). So your first action will be checking if the target columns types are actually nvarchar (or nchar).
Then, let's assume that all input strings are UTF-8 encoded in your PHP script. You want to execute something like
$stmt->bindParam(':text', $utf8_encoded_text);
According to the documentation, UTF-8 is the default string encoding. I hope it's smart enough to work with NVARCHAR, otherwise you may need to use the extra options.
Your colleague's solution doesn't store Unicode strings: it converts in the ISO-8859-1 space, then saves the bytes in simple CHAR or VARCHAR columns. The difference is that you won't be able to store character outside of the ISO-8859-1 space (eg Polish)
Take a look at this article on "Handling Unicode Front to Back in a Web App". By far one of the best articles I've seen on the subject. If you follow the guide and the issues are still present, then you know for sure that it's not your fault.
I am writing a parser. I have taken care of all the encoding conversion to output UTF-8 correctly, but sometimes the source material is incorrect. such as ☐ or â€tm - the results of bad encoding conversion.
I know this is a long shot - but does anyone know of a list of common strings resulting from bad character conversions, or anything so I don't have to build my own list.
Yes I know I am being lazy, but I read somewhere that makes me a good programmer?
tl;dr: See last two paragraphs.
I hate/love encoding problems.
We're looking at a mutated copy of Unicode Character 'RIGHT SINGLE QUOTATION MARK' (U+2019). The byte sequence for that character is 0xE2 0x80 0x99. In Windows-1252, that corresponds to a+hat, Euro, and the trademark symbol (™). The 'tm' we see is a further transliteration of that trademark symbol into ASCII t and ASCII m, 0x74 0x6D, making our final corrupted sequence of bytes 0xE2 0x80 0x74 0x6D.
Chances are that the actual representation of a+hat-euro-t-m is already in UTF-8. That is, that a+hat is a UTF-8 sequence and the Euro symbol is also a UTF-8 sequence, because someone Copied from a Windows-1252 document that was already improperly encoded, and Pasted into a UTF-8 document. You'll find it's plenty more bytes than just the four from the original corruption.
One way to solve this would be first turning the UTF-8 encoding of those characters back into Windows-1252, then treat that Windows-1252 string as UTF-8 when writing it back out.
You can use iconv with the //TRANSLIT flag for this purpose:
$less_bad = iconv('UTF-8', 'Windows-1252//TRANSLIT', $bad);
This tells iconv to try turning any characters that can't be represented in Windows-1252 into something similar. This translation is imperfect and will destroy any legitimate UTF-8 characters that aren't representable in Windows-1252.
Once you have the Windows-1252 string, save it back out and serve it up as UTF-8. If all went well, the corruption should be gone, and you shouldn't have any problems.
Yeah, right.
In this specific case, the final byte of the proper sequence, 0x99, has been munged into two bytes by a bad Copy/Paste. You aren't going to get it back through character set encoding hoop jumping.
While the hoop jumping could work for some documents, you will surely find many things that are even more poorly re-encoded. Your best bet is going to be conducting a byte-level search and replace operation, looking for incorrectly encoded sequences and replacing them with a plain-ASCII or properly UTF-8 encoded alternative. There are lots of ways that the encoding would be wrong. For example, if the corruption source was in the ISO-8859 family, the final corrupted sequence would have been different, or perhaps the final ™ might not be munched into t and m in certain places.
A byte-level search and replace is guaranteed only to impact incorrectly re-encoded sequences, and will not leave the risk of munching on single-encoded UTF-8 characters that can't be represented in inferior character sets. It's safer and faster.
edit: I totally didn't actually catch that you were already planning on doing this. ;) Unfortunately I've never seen such a handy list. Perhaps you should publish and publicize your work so that others may benefit. yourcharacterencodingsucks.com is available!
I am generating a csv file through php to be downloaded through the browser.
Do I need to insert the byte order mark bytes in the beginning, considering the target system that would be used can be a mac,unix , windows , etc ?
No, you are not required to.
Byte Order Mark is used in some Unicode encodings, namely UTF-8, UTF-16 and UTF-32 to determine that the encoding is really Unicode.
In UTF-16, it is used to differentiate UTF-16 from UCS-2 (a subset of UTF-16).
It is optional in UTF-8 and UTF-32, but valid. However, in UTF-8, it can cause compatibility issues. To quote a well-phrased Wikipedia entry:
If compatibility with existing
programs is not important, the BOM
could be used to identify if a file is
in UTF-8 versus a legacy encoding, but
this is still problematic, due to many
instances where the BOM is added or
removed without actually changing the
encoding, or various encodings are
concatenated together. Checking if the
text is valid UTF-8 is more reliable
than using BOM.
I would go against using the BOM in UTF-8 for those reasons.
Concerning the original question, it is really up to the way that file is encoded when written. If it will be utf-8 encoded i'd add the BOM. If there are just ASCII characters within the file, the BOM can be absent because there will be no sequences. If however utf-8 sequences are within the file, it will be more easy to detect the BOM as to walk through the whole file and check for valid sequences. And even if you detect a single sequence, it still might be single characters above 0x7F.