How to remove non-Chinese characters from strings in PHP using regular expressions

Regular expression is a tool used to describe and match string patterns. It can be used in PHP to perform string processing operations, such as deleting non-Chinese characters. Here we will introduce how to use regular expressions to remove non-Chinese characters in strings.

First, we need to understand some basic regular expression syntax. In PHP, regular expressions start and end with a slash /, for example: /pattern/, where pattern is the pattern we want to match. The following are some commonly used regular expression character classes:

1. d matches numeric characters
2. D matches non-numeric characters
3. w matches alphanumeric characters, including underscore
4. W Matches non-alphanumeric characters, excluding underscores
5. s Matches whitespace characters, including spaces, tabs, and newlines
6. S ​​Matches non-whitespace characters
7. . Matches any character, except newline character

In PHP, we can use the preg_replace function to perform string replacement. The syntax of this function is as follows:

preg_replace ( mixed $pattern , mixed $replacement , mixed $subject [, int $limit = -1 [, int &$count ]] ) : mixed

Among them, $pattern represents the pattern to be matched, $replacement represents the string to be replaced, and $subject represents the target string to be replaced. The following is an example:

$str = "Hello, this is a test.";
$str = preg_replace('/test/', 'example', $str);
echo $str; // 输出：Hello, this is a example.

Now let us solve the problem of deleting non-Chinese characters in the string. In order to achieve this function, we can add regular expressions of non-Chinese characters to the preg_replace function and replace them with empty strings. The following is an example of a regular expression that matches non-Chinese characters:

/[^x{4e00}-x{9fa5}]/u

This regular expression uses Unicode encoding, where x represents a hexadecimal number, {4e00} to {9fa5} are Chinese characters in Unicode coding range.

Next, we can use the preg_replace function to replace non-Chinese characters with an empty string:

$str = "Hello, 你好！This is a test.";
$str = preg_replace('/[^x{4e00}-x{9fa5}]/u', '', $str);
echo $str; // 输出：你好

In the above example, the regular expression is included between two slashes , and the /u option is used, indicating that Unicode encoding is used for matching.

Through the above example, we can see that it is very simple to use regular expressions to delete non-Chinese characters in a string. All you need to do is create a regular expression specifying the character set that needs to be removed, and then use the preg_replace function to replace it with an empty string.

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