Unicode, UTF, ASCII, ANSI format differences
What is the difference between the
In what way are these helpful for programmers?
Going down your list:
- "Unicode" isn't an encoding, although unfortunately, a lot of documentation imprecisely uses it to refer to whichever Unicode encoding that particular system uses by default. On Windows and Java, this often means UTF-16; in many other places, it means UTF-8. Properly, Unicode refers to the abstract character set itself, not to any particular encoding.
- UTF-16: 2 bytes per "code unit". This is the native format of strings in .NET, and generally in Windows and Java. Values outside the Basic Multilingual Plane (BMP) are encoded as surrogate pairs. These used to be relatively rarely used, but now many consumer applications will need to be aware of non-BMP characters in order to support emojis.
- UTF-8: Variable length encoding, 1-4 bytes per code point. ASCII values are encoded as ASCII using 1 byte.
- UTF-7: Usually used for mail encoding. Chances are if you think you need it and you're not doing mail, you're wrong. (That's just my experience of people posting in newsgroups etc - outside mail, it's really not widely used at all.)
- UTF-32: Fixed width encoding using 4 bytes per code point. This isn't very efficient, but makes life easier outside the BMP. I have a .NET
Utf32Stringclass as part of my MiscUtil library, should you ever want it. (It's not been very thoroughly tested, mind you.)
- ASCII: Single byte encoding only using the bottom 7 bits. (Unicode code points 0-127.) No accents etc.
- ANSI: There's no one fixed ANSI encoding - there are lots of them. Usually when people say "ANSI" they mean "the default locale/codepage for my system" which is obtained via Encoding.Default, and is often Windows-1252 but can be other locales.
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Some reading to get you started on character encodings: Joel on Software: The Absolute Minimum Every Software Developer Absolutely, Positively Must Know About Unicode and Character Sets (No Excuses!)
By the way - ASP.NET has nothing to do with it. Encodings are universal.