Briefly talk about unicode and utf8 encoding in php, unicodeutf8_PHP tutorial

Briefly talk about unicode and utf8 encoding in php, unicodeutf8

Re-understand unicode and utf8 encoding

Until today, just now to be precise, I didn’t know that UTF-8 encoding and Unicode encoding are different, there is a difference 囧
There is a certain connection between them, look at their differences:
The length of UTF-8 is not certain, it may be 1, 2, or 3 bytes
Unicode has a certain length, 2 bytes (USC-2)
UTF-8 can be converted to and from Unicode

The relationship between unicode and utf8

Unicode(16)

UTF-8(binary)

0000 - 007F 0xxxxxxx
0080 - 07FF 110xxxxx 10xxxxxx
0800 - FFFF 1110xxxx 10xxxxxx 10xxxxxx

The above table has two meanings. The first one is obviously the correspondence between Unicode and UTF-8 character ranges, and the other one shows how Unicode and UTF-8 are converted to each other:

Let’s talk about UTF-8 to Unicode conversion first

The UTF-8 encoded binary is matched with the above three formats. After matching, the fixed bits (non-x positions in the table) are removed, and then every 8 bits are grouped from right to left. If there are not enough 8 bits, the left side will not be used. , make up 2 bytes and 16 bits. These 16 bits represent the Unicode encoding corresponding to UTF-8. Take a look at the following examples:

The text encoding format in the above picture is UTF-8, and you can use WinHex to see its hexadecimal representation
Copy code The code is as follows:
Character => UTF-8 => UTF-8 binary => Remove the fixed position to make up the 16-bit binary => Hexadecimal

Chinese => E6B189 => 11100110 10110001 10001001 => 01101100 01001001 => 6C49
Word => E5AD97 => 11100101 10101101 10010111 => 01011011 01010111 => 5B57

#The following is the result of running under the chrome command line
'u6C49'
"汉"
'u5B57'
"Word"

#At this point, converting from UTF-8 to Unicode is already a very easy task. Take a look at the pseudocode of the conversion
Read one byte, 11100110
Determine the format of the UTF-8 character, which belongs to the third type, 3 bytes
Continue reading 2 bytes to get 11100101 10101101 10010111
Remove the fixed bits according to the format 1011011 01010111
Not enough 16 digits, add zeros on the left 01011011 01010111 => 5B57

Look again at the conversion from Unicode to UTF-8

Copy code The code is as follows:
5B57
Get the Unicode range where 5B57 is located, 0800 Get the binary encoding of 5B57 101101101010111
Use the binary encoding in the previous step to splice UTF-8 encoding from right to left 11100101 10101101 10010111

Talk about the problem

Let’s talk about the cause of today’s problem. Many words are input from the front end. Each word in UTF-8 format has a maximum of 30 bytes, so verification will be done on the front end and backend respectively. JavaScript uses Unicode encoding, and the backend program UTF-8 encoding is used, and the current solution is as follows

Front end

function utf8_bytes(str)
{
 var len = 0, unicode;
 for(var i = 0; i < str.length; i++)
 {
 unicode = str.charCodeAt(i);
 if(unicode < 0x0080) {
  ++len;
 } else if(unicode < 0x0800) {
  len += 2;
 } else if(unicode <= 0xFFFF) {
  len += 3;
 }else {
  throw "characters must be USC-2!!"
 }
 }
 return len;
}

#例子
utf8_bytes('asdasdas')
8
utf8_bytes('yrt燕睿涛')
12

Backstage

#对于GBK字符串
$len = ceil(strlen(bin2hex(iconv('GBK', 'UTF-8', $word)))/2);
#对于UTF8字符串
$len = ceil(strlen(bin2hex($word))/2);

The above is the entire content of this article, I hope you all like it.

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