Regarding the parameter passing problem of php preg_replace_callback callback function

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preg_replace_callback

The function of this function is to perform a regular expression search and use a callback Replace

preg_replace_callback ( mixed $pattern , callable $callback , mixed $subject [, int $limit = -1 [, int &$count ]] ) : mixed

Parameter description

• pattern

The pattern to be searched can be a string or a string array .

• callback

A callback function that is called every time a replacement is needed. The parameters obtained by the function when called are matched from the subject. result. The callback function returns the string that actually participates in the replacement. This is the signature of the callback function:

• handler ( array $matches ) : string

The callback function is often needed and is only used for preg_replace_callback () a local call. In this case, you can use anonymous function to define an anonymous function as a callback when preg_replace_callback() is called. This way you keep all the calling information in the same place and don't pollute the function namespace with a callback function name that isn't used anywhere else.

Example #1 preg_replace_callback() and anonymous function

<?php
/* 一个unix样式的命令行过滤器，用于将段落开始部分的大写字母转换为小写。 */
$fp = fopen("php://stdin", "r") or die("can&#39;t read stdin");
while (!feof($fp)) {
    $line = fgets($fp);
    $line = preg_replace_callback(
        &#39;|<p>\s*\w|&#39;,
        function ($matches) {
            return strtolower($matches[0]);
        },
        $line
    );
    echo $line;
}
fclose($fp);
?>

• subject

The target string or character to be searched for and replaced string array.

• limit

The maximum number of substitutions that can be used for each subject string per pattern. Default is -1 (no limit).

• count

If specified, this variable will be filled with the number of times the replacement was performed.

How to pass parameters

By default, this callback function will only receive the $matches matching parameter. If we want to pass more parameters, we can use detours Tactics, as the saying goes, all roads lead to Rome, as long as we can access the parameters that need to be passed in the anonymous function. So we have two options.

1. Use global variables

$param1 = "test";
preg_replace_callback($pregRule, function ($match) {
    global $param1;
    return $match[1] . $param1 . $match[3];
}

2. Use object-oriented loading classes

class Scrapy{
   private $param1 = "test";
   public function info(){
      preg_replace_callback($pregRule, function ($match) {
            return $match[1] . $this->param1 . $match[3];
        }
   }
}

Through the above two methods, we can call the callback function we want to pass input parameters.

Summary

There are always more solutions than problems. If you encounter a problem that cannot be solved, if you change your thinking, you may have a bright future.

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