在标记中为每个表添加类名

Question

In PHP I need to search through my $post content and find all the opening <table> tags to add a unique class name based on its index. I know the code below is wrong but hopefully gets the point across.

$content = '<table></table><p></p><table></table><p></p><table></table><p></p>';
preg_match_all('/find all <table> tags/', $content, $matches);
for ($i=0; $i < count($matches); $i++) {
    $new_value = '<table class=""' . $i . ' >'; 
    str_replace( $matches[$i], $new_value, $content);
}

Answer 1

The better way is using a DOM parser. With Regular Expressions you are able to do this simple task without a mess but for right tool's sake, do it with a parser:

$dom = new DOMDocument();
libxml_use_internal_errors(true);
$dom->loadHTML($content, LIBXML_HTML_NOIMPLIED | LIBXML_HTML_NODEFDTD);
libxml_use_internal_errors(false);
$tables = $dom->getElementsByTagName('table');

foreach ($tables as $i => $table) {
    $table->setAttribute('class', "table_$i");
}

echo $dom->saveHTML();

Live demo

RegEx solution, not preferred

$counter = 0;
echo preg_replace_callback('~<table\K>~', function() use (&$counter) {
    return ' class="table_' . $counter++ . '">';
}, $content);

Live demo