preg_replace: Remove comments only within curly backets

Question

I have this:

$text = 'This is some text /*Comment 1 */ . Some more text{ This is to let you know that /* this is a comment*/. A comment /*this one is */ can be anything }. So the next thing { This is to let you know that /*  this is a comment*/. A comment /*this one is */ can be anything } is another topic. /*Final comment*/';

Need this:

$text = 'This is some text /*Comment 1 */ . Some more text{ This is to let you know that . A comment  can be anything }. So the next thing { This is to let you know that . A comment  can be anything } is another topic. /*Final comment*/';

Tried this:

$text = preg_replace("/\/\*.*?\*\//", "", $text);

The problem is that what I have tried, is removing all the comments. I just want the comments appearing within { } to be removed. How to do this?

Haven't thought of it. Such kind of data is unexpected. What would be a possible solution in such a case? — Devner
– Devner, Commented Apr 1, 2012 at 6:44
It’s all up to you. But it’s a case that you should consider when defining such a language. — Gumbo
– Gumbo, Commented Apr 1, 2012 at 6:47

Gumbo · Accepted Answer · 2012-04-01 05:48:58Z

2

You can use the following regular expression to tokenize the string:

$tokens = preg_split('~(/\*.*?\*/|[{}])~s', $str, -1, PREG_SPLIT_DELIM_CAPTURE);

Then iterate the tokens to find opening { and the comments inside them:

$level = 0;
for ($i=1, $n=count($tokens); $i<$n; $i+=2) {  // iterate only the special tokens
    $token = &$tokens[$i];
    switch ($token) {
    case '{':
        $level++;
        break;
    case '}':
        if ($level < 1) {
            echo 'parse error: unexpected "}"';
            break 2;
       }
       $level--;
       break;
   default:  // since we only have four different tokens, this must be a comment
       if ($level > 0) {
           unset($tokens[$i]);
       }
       break;
   }
}
if ($level > 0) {
    echo 'parse error: expecting "}"';
} else {
    $str = implode('', $tokens);
}

answered Apr 1, 2012 at 5:48

Gumbo

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1 Comment

Devner Over a year ago

+1 Because even this is a working solution. Your level of understanding of how this works is a lot more than me. And because I cant accept 2 posts as an answer, I am voting this up.

Aram Kocharyan · Accepted Answer · 2012-04-01 05:48:13Z

0

This is probably the safest way:

<?php

$text = 'This is some text /*Comment 1 */ . Some more text{ This is to let you know that /* this is a comment*/. A comment /*this one is */ can be anything }. So the next thing { This is to let you know that /*  this is a comment*/. A comment /*this one is */ can be anything } is another topic. /*Final comment*/';

$text = preg_replace_callback('#\{[^}]+\}#msi', 'remove_comments', $text);

var_dump($text);

function remove_comments($text) {
    return preg_replace('#/\*.*?\*/#msi', '', $text[0]);
}

?>

It searches for {} then removes the comments inside them. This will remove multiple comments in a {}.

answered Apr 1, 2012 at 5:48

Aram Kocharyan

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