php 正则表达式

// 用preg_match 模仿实现 preg_match_all

function custom_preg_match_all($pattern, $subject)

{

    $offset = 0;

    $match_count = 0;

    while(preg_match($pattern, $subject, $matches, PREG_OFFSET_CAPTURE, $offset))

    {

        // Increment counter

        $match_count++;

    

        // Get byte offset and byte length (assuming single byte encoded)

        $match_start = $matches[0][1];

        $match_length = strlen($matches[0][0]);



        // (Optional) Transform $matches to the format it is usually set as (without PREG_OFFSET_CAPTURE set)

        foreach($matches as $k => $match) $newmatches[$k] = $match[0];

        $matches = $newmatches;

    

        // Your code here

        echo "Match number $match_count, at byte offset $match_start, $match_length bytes long: ".$matches[0]."\r\n";

            

        // Update offset to the end of the match

        $offset = $match_start + $match_length;

    }



    return $match_count;

}

　正则匹配练习：

文本源： <div>2</div> 2<div>1</div>abcd

模式1：
<div>.*</div>
匹配结果：
<div>2</div> 2<div>1</div>

模式2
<div>.*?</div>
匹配结果：
<div>2</div>
<div>1</div>

对于模式2，如果文本源变为：
<div><div>2</div> 2<div>1</div>abcd
匹配结果：
Match 1: <div><div>2</div> 1 17
Match 2: <div>1</div> 20 12
显然有问题；
解决办法：
模式3：
<div>((?!</?div>).)*</div>
匹配结果：
Match 1: <div>2</div> 5 12
Group 1: 2 10 1
Match 2: <div>1</div> 19 12
Group 1: 1 24 1