Convert Single Line Comments To Block Comments - php

Question

I need to convert single line comments (//...) to block comments (/*...*/). I have nearly accomplished this in the following code; however, I need the function to skip any single line comment is already in a block comment. Currently it matches any single line comment, even when the single line comment is in a block comment.
## Convert Single Line Comment to Block Comments
function singleLineComments( &$output ) {
$output = preg_replace_callback('#//(.*)#m',
create_function(
'$match',
'return "/* " . trim(mb_substr($match[1], 0)) . " */";'
), $output
);
}

Answer 1

As already mentioned, "//..." can occur inside block comments and string literals. So if you create a small "parser" with the aid f a bit of regex-trickery, you could first match either of those things (string literals or block-comments), and after that, test if "//..." is present.
Here's a small demo:
$code ='A
B
// okay!
/*
C
D
// ignore me E F G
H
*/
I
// yes!
K
L = "foo // bar // string";
done // one more!';
$regex = '#
("(?:\\.|[^\r\n\\"])*+") # group 1: matches double quoted string literals
|
(/\*[\s\S]*?\*/) # group 2: matches multi-line comment blocks
|
(//[^\r\n]*+) # group 3: matches single line comments
#x';
preg_match_all($regex, $code, $matches, PREG_SET_ORDER | PREG_OFFSET_CAPTURE);
foreach($matches as $m) {
if(isset($m[3])) {
echo "replace the string '{$m[3][0]}' starting at offset: {$m[3][1]}\n";
}
}
Which produces the following output:
replace the string '// okay!' starting at offset: 6
replace the string '// yes!' starting at offset: 56
replace the string '// one more!' starting at offset: 102
Of course, there are more string literals possible in PHP, but you get my drift, I presume.
HTH.

Answer 2

You could try a negative look behind: http://www.regular-expressions.info/lookaround.html
## Convert Single Line Comment to Block Comments
function sinlgeLineComments( &$output ) {
$output = preg_replace_callback('#^((?:(?!/\*).)*?)//(.*)#m',
create_function(
'$match',
'return "/* " . trim(mb_substr($match[1], 0)) . " */";'
), $output
);
}
however I worry about possible strings with // in them. like:
$x = "some string // with slashes";
Would get converted.
If your source file is PHP, you could use tokenizer to parse the file with better precision.
http://php.net/manual/en/tokenizer.examples.php
Edit:
Forgot about the fixed length, which you can overcome by nesting the expression. The above should work now. I tested it with:
$foo = "// this is foo";
sinlgeLineComments($foo);
echo $foo . "\n";
$foo2 = "/* something // this is foo2 */";
sinlgeLineComments($foo2);
echo $foo2 . "\n";
$foo3 = "the quick brown fox";
sinlgeLineComments($foo3);
echo $foo3. "\n";;