over 2 years ago

Let me use an example to illustrate this topic:

A chinese character:      汉
it's unicode value:       U+6C49
convert 6C49 to binary:   01101100 01001001

Nothing magical so far, it's very simple. Now, let's say we decide to store this character on our hard drive. To do that, we need to store the character in binary format. We can simply store it as is '01101100 01001001'. Done!

But wait a minute, is '01101100 01001001' one character or two characters? You knew this is one character because I told you, but when a computer reads it, it has no idea. So we need some sort of "encoding" to tell the computer to treat it as one.

This is where the rules of 'UTF-8' comes in: http://www.fileformat.info/info/unicode/utf8.htm

Binary format of bytes in sequence

1st Byte    2nd Byte    3rd Byte    4th Byte    Number of Free Bits   Maximum Expressible Unicode Value
0xxxxxxx                                                7             007F hex (127)
110xxxxx    10xxxxxx                                (5+6)=11          07FF hex (2047)
1110xxxx    10xxxxxx    10xxxxxx                  (4+6+6)=16          FFFF hex (65535)
11110xxx    10xxxxxx    10xxxxxx    10xxxxxx    (3+6+6+6)=21          10FFFF hex (1,114,111)

According to the table above, if we want to store this character using the 'UTF-8' format, we need to prefix our character with some 'headers'. Our chinese character is 16 bits long (count the binary value yourself), so we will use the format on row 3 as it provides enough space:

Header  Place holder    Fill in our Binary   Result         
1110    xxxx            0110                 11100110
10      xxxxxx          110001               10110001
10      xxxxxx          001001               10001001

Writing out the result in one line:

11100110 10110001 10001001

This is the UTF-8 (binary) value of the chinese character! (confirm it yourself)

Summary

A chinese character:      汉
it's unicode value:       U+6C49
convert 6C49 to binary:   01101100 01001001
UTF-8 binary:             11100110 10110001 10001001
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