获取Undefined属性：在WordPress插件中的DOM内部使用JSON时出现stdClass :: $ key错误

In the main functions.php file of my WordPress plugin I use the following code

<?php
$str = '{"p_0":"New first content"}';
$json = json_decode($str);

$html = '<p>First</p><p>Second</p>';
$dom = new DOMDocument;
$html = mb_convert_encoding($html, 'HTML-ENTITIES', 'UTF-8');
libxml_use_internal_errors(true);
$dom->loadHTML($html);
libxml_use_internal_errors(false);

foreach($dom->getElementsByTagName('p') as $index => $p) {
    $p->setAttribute('id','p_'.$index);
    $id = $p->getAttribute('id');
    if($json->{$id}) {
        $p->nodeValue = $json->{$id};
    }
}

echo $dom->saveXML($dom);
?>

The first paragraph is overriden but at that I get the error

Undefined property: stdClass::$p_0 in ... // the line where if($json->{$id})

How can I avoid the error?

You have only one p_0 object and you are trying to access p_1 which does not exist in your $str

Now if you just want to avoid error then you can use isset()

you can replace if condition like this

if(isset($json->{$id})) {
    $p->nodeValue = $json->{$id};
}