Understanding Character Encoding

07 Feb, 2018
Ever imagined how a computer is able to understand and display what you have written? Ever wondered what a UTF-8 or UTF-16 meant when you were going through some configurations? Just think about how “HeLLo WorlD” should be interpreted by a computer.We all know that a computer stores data in bits and bytes. So, to display a character on screen or map the character as a byte in memory of the computer needs to have a standard. Read the following :
\x48\x65\x4C\x4C\x6F\x20\x57\x6F\x72\x6C\x44
This is something a memory would show you. How do you know what character each memory byte specifies?
Here comes character encoding into the picture:
If you have already not guessed it – Its “HeLLo WorlD” in UTF-8 for you. And yes, we will go ahead and read about UTF-8. But let’s start with ASCII. Most of you who have done programming or worked with strings must have known what ASCII is. If you haven’t then let’s define what ASCII is.ASCII: ASCII stands for American Standard Code for Information Interchange. Computers can only understand numbers, so an ASCII code is the numerical representation of a character such as ‘a’ or ‘@’ or an action of some sort. ASCII was developed a long time ago and now the non-printing characters are rarely used for their original purpose.
Just look at the following –
And so on. You can look at the ASCII table and mapping at http://www.asciitable.com/. If you have not already looked at the table, I will recommend that you do it now! You will observe that these are a simple set of English words and punctuations.
Now Suppose I want to write the below characters: 
AB?@
This will be interpreted by my decoder as 0x410x0a0x200x420x3f0x40 in hex and 065010032066063064 in decimal, where even a space (0x20) and a next line (0x0a) has a byte value or a memory space.
Different countries, languages but the need that brought them together 
Today internet has made the world come close together. And the people all over the world do not speak just English, right? There came a need to expand this space. If you have created an application and you see that people in France want to use it as you see a high potential there. Wouldn’t it be nice to just have a change in language but having the same functionality?
Why not create a Universal Code in short Unicode for everyone ??
So, here came the Unicode with a really good idea. It assigned every character, including different languages, a unique number called Code Point. One advantage of Unicode over other possible sets is that its first 256 code points are identical to ASCII. So for a software/browser it is easier to encode and decode characters of majority of living languages in use on computers. It aims to be, and to a large extent already is, a superset of all other character sets that have been encoded.
Unicode also is a character set (not an encoding). It uses the same characters like the ASCII standard, but it extends the list with additional characters, which gives each character a Code point. It has the ambition to contain all characters (and popular icons) used in the entire world.
Before knowing these let us get a few terminologies straight :
A character is a minimal unit of text that has semantic value.
A character set is a collection of characters that might be used by multiple languages. Example: The Latin character set is used by English and most European languages, though the Greek character set is used only by the Greek language.
A coded character set is a character set in which each character corresponds to a unique number.
A code point of a coded character set is any legal value in the character set.
A code unit is a bit sequence used to encode each character of a repertoire within a given encoding form.
Ever wondered what is UTF-8 or UTF-16??
UTF-8: UTF-8 has truly been the dominant character encoding for the World Wide Web since 2009, and as of June 2017 accounts for 89.4% of all Web pages. UTF-8 encodes each of the 1,112,064 valid code points in Unicode using one to four 8-bit bytes. Code points with lower numerical values, which tend to occur more frequently, are encoded using fewer bytes. The first 128 characters of Unicode, which correspond one-to-one with ASCII, are encoded using a single octet with the same binary value as ASCII, so that valid ASCII text is valid UTF-8-encoded Unicode as well.
So how many bytes give access to what characters in these encodings?UTF-8:1 byte: Standard ASCII2 bytes: Arabic, Hebrew, most European scripts (most notably excluding Georgian)3 bytes: BMP4 bytes: All Unicode characters
UTF-16:2 bytes: BMP4 bytes: All Unicode characters
So I did make a mention about BMP. What is it exactly?
Basic Multilingual Plane (BMP) contains characters for almost all modern languages, and a large number of symbols. A primary objective for the BMP is to support the unification of prior character sets as well as characters for writing.
UTF-8, UTF-16 and UTF-32 are encodings that apply the Unicode character table. But they each have a slightly different way on how to encode them. UTF-8 will only use 1 byte when encoding an ASCII character, giving the same output as any other ASCII encoding. But for other characters, it will use the first bit to indicate that a 2nd byte will follow. UTF-16 uses 16-bit by default, but that only gives you 65k possible characters, which is nowhere near enough for the full Unicode set. So some characters use pairs of 16-bit values. UTF-32 is opposite, it uses the most memory (each character is a fixed 4 bytes wide), which makes it quite bloated but now in this scenario every character has this precise length, so string manipulation becomes far simpler. You can compute the number of characters in a string simply from the length in bytes of the string. You can’t do that with UTF-8.This is how it eases to accommodate the entire character set for different languages and help people spread their applications or information to the world just coding/writing in their language rest all is taken care by the Decoder.
As this being just the beginning into the world of Character Encoding. I hope this helps you understand Character encoding at a higher level.
This article is contributed by Deepa Banerjee. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
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