Here are examples of the BOM usage that actually cause real problems and yet many people don't know about it. Show
BOM breaks scriptsShell 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:
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:
BOM is illegal in JSONSee RFC 7159, Section 8.1:
BOM is redundant in JSONNot 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 parsersNot 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:
Now, if the file starts with BOM it will look like this:
Note that:
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 formatsBOM 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 BOMAs 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. The character set support in PostgreSQL allows you to store text in a variety of character sets (also called encodings), including single-byte character sets such as the ISO 8859 series and multiple-byte character sets such as EUC (Extended Unix Code), UTF-8, and Mule internal code. All supported character sets can be used transparently by clients, but a few are not supported for use within the server (that is, as a server-side encoding).
The default character set is selected while initializing your PostgreSQL database cluster using An important restriction, however, is that each database's character set must be compatible with the database's 24.3.1. Supported Character SetsTable 24.1 shows the character sets available for use in PostgreSQL. Table 24.1. PostgreSQL Character Sets
Not all client APIs support all the listed character sets. For example, the PostgreSQL JDBC driver does not support The 24.3.2. Setting the Character Set
initdb -E EUC_JP sets the default character set to You can specify a non-default encoding at database creation time, provided that the encoding is compatible with the selected locale: createdb -E EUC_KR -T template0 --lc-collate=ko_KR.euckr --lc-ctype=ko_KR.euckr korean This will create a database named CREATE DATABASE korean WITH ENCODING 'EUC_KR' LC_COLLATE='ko_KR.euckr' LC_CTYPE='ko_KR.euckr' TEMPLATE=template0; Notice that the above commands specify copying the The encoding for a database is stored in the system catalog $ ImportantOn most modern operating systems, PostgreSQL can determine which character set is implied by the PostgreSQL will allow superusers to create databases with 24.3.3. Automatic Character Set Conversion Between Server and ClientPostgreSQL supports automatic character set conversion between server and client for many combinations of character sets (Section 24.3.4 shows which ones). To enable automatic character set conversion, you have to tell PostgreSQL the character set (encoding) you would like to use in the client. There are several ways to accomplish this:
If the conversion of a particular character is not possible — suppose you chose If the client character set is defined as 24.3.4. Available Character Set ConversionsPostgreSQL allows conversion between any two character sets for which a conversion function is listed in the Table 24.2. Built-in Client/Server Character Set Conversions
Table 24.3. All Built-in Character Set Conversions
24.3.5. Further ReadingThese are good sources to start learning about various kinds of encoding systems. CJKV Information Processing: Chinese, Japanese, Korean & Vietnamese Computing Contains detailed explanations of The web site of the Unicode Consortium. RFC 3629UTF-8 (8-bit UCS/Unicode Transformation Format) is defined here. How do you extract a single character from a String you can refer directly to an individual character via the method?charAt() To extract a single character from a String, you can refer directly to an individual character via the charAt() method.
Which of these methods can be used to convert all characters in a String into a character array Mcq?Explanation: Because we are performing operation on reference variable which is null. 5. Which of these methods can be used to convert all characters in a String into a character array? Explanation: charAt() return one character only not array of character.
Which of the following method is used to convert a String into an array?Using toArray() Method
The toArray() function of the List class can also be used to convert a string to array in Java. It takes a list of type String as the input and converts each entity into an element of a string array.
How do I extract a character from a String in java?Using String.. Get the string and the index.. Convert the String into Character array using String. toCharArray() method.. Get the specific character at the specific index of the character array.. Return the specific character.. |