Detailed explanation of PHP string encoding issues

As we all know, different character encodings occupy different numbers of bytes in memory. For example, ASCII encoded characters occupy 1 byte, UTF-8 encoded Chinese characters are 3 bytes, and GBK are 2 bytes. PHP also comes with several string interception functions, among which substr and mb_substr are commonly used.

When using substr to intercept Chinese characters, garbled characters will appear. This is because substr is intercepted by bytes. That is, UTF-8 encoded Chinese, using substr to intercept, will only intercept 1/3 of the Chinese, and of course garbled characters will appear.

The parameter $encoding in mb_substr ( string $str , int $start [, int $length [, string $encoding ]] ) can specify the encoding. If omitted, the internal character encoding is used.

If you don’t know the encoding format of the string, you can use mb_detect_encoding to check:

$encoding = mb_detect_encoding($string, array("ASCII",'UTF-8′,"GB2312′ ,"GBK",'BIG5′));

Then:

mb_substr ( string $str , int $start [, int $length [, string $encoding ]] )

If you implement mb_substr by yourself, the efficiency is not very good.

Encoding-related php functions use

ord(substr($str, $i, 1)) > 0xa0)

ord($string) returns the ASC code of the first character of the string. This can be used to determine whether the first character of the intercepted string is a Chinese character, because for example, a text encoded by gb2312 is 2 bytes, utf8 It is three bytes. That is, the encoding is greater than 256 Chinese characters.

Regular characters:

Matching Chinese characters: preg_match_all('/[\x80-\xff]?./', $string , $match);

Match English: preg_match_all("/[/x01-/x7f]+/", $string, $match);

Encoding conversion

iconv ( string $in_charset , string $out_charset , string $str )

Such as GB2312 to UTF-8: iconv("GB2312","UTF-8",$text)

url encoding All non-alphanumeric characters except -_. in the string returned by urlencode

will be replaced with a percent sign (%) followed by two hexadecimal digits, and spaces will be encoded as plus sign (+). The encoding method of WWW form POST data is the same, and the media type encoding method of application/x-www-form-urlencoded is the same.

However, it should be noted that only part of the URL should be encoded when encoding, otherwise the colons and backslashes in the URL will also be escaped.

There are generally two methods of URLEncode, one is the traditional Encode based on GB2312, and the other is the Encode based on UTF-8. For example:

$url = '中国';
echo urlencode($url );
//UTF-8: %E4%B8%AD%E5%9B%BD
//GB2312:%D6%D0%B9%FA

For example, we use the browser to open Baidu and search for "China". In the address bar, we see:

http://www.baidu.com/s?wd=%E4 %B8%AD%E5%9B%BD&rsv_bp=0&ch=&tn=baidu&bar=&rsv_spt=3&ie=utf-8&rsv_sug3=16&rsv_sug=0&rsv_sug4=302&rsv_sug1=11&inputT=22928

That is, we see "China" being used by the browser Automatically converted to: %E4%B8%AD%E5%9B%BD.

The difference between urlencode and rawurlencode: urlencode encodes spaces as a plus sign "+", and rawurlencode encodes spaces as a plus sign "%20".

url decoding urldecode and rawurldecode

1. When decoding, you can use the corresponding urldecode() and rawurldecode(), accordingly, rawurldecode() does not decode the plus sign ('+') into a space, while urldecode() does.

2. The decoded string of urldecode() and rawurldecode() is encoded in UTF-8 format. If the URL contains non-UTF-8 encoded Chinese, the decoded string must be converted. .

As follows, first set the php file to gb2312 encoding. You will see that part of it is garbled and part of it is normal.

$url = '中国';
echo $a = urldecode(urlencode($url)) ,' ';
echo iconv('gb2312', 'utf-8', $a);

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