Erasing C comments with preg_replace - php

Question

I need to erase all comments in $string which contains data from some C file.
The thing I need to replace looks like this:
something before that shouldnt be replaced
/*
* some text in between with / or * on many lines
*/
something after that shouldnt be replaced
and the result should look like this:
something before that shouldnt be replaced
something after that shouldnt be replaced
I have tried many regular expressions but neither work the way I need.
Here are some latest ones:
$string = preg_replace("/\/\*(.*?)\*\//u", "", $string);
and
$string = preg_replace("/\/\*[^\*\/]*\*\//u", "", $string);
Note: the text is in UTF-8, the string can contain multibyte characters.

Answer 1

You would also want to add the s modifier to tell the regex that .* should include newlines. I always think of s to mean "treat the input text as a single line"
So something like this should work:
$string = preg_replace("/\\/\\*(.*?)\\*\\//us", "", $string);
Example: http://codepad.viper-7.com/XVo9Tp
Edit: Added extra escape slashes to the regex as Brandin suggested because he is right.

Answer 2

I don't think regexp fit good here. What about wrote a very small parse to remove this? I don't do PHP coding for a long time. So, I will try to just give you the idea (simple alogorithm) I haven't tested this, it's just to you get the idea, as I said:
buf = new String() // hold the source code without comments
pos = 0
while(string[pos] != EOF) {
if(string[pos] == '/') {
pos++;
while(string[pos] != EOF)
{
if(string[pos] == '*' && string[pos + 1] == '/') {
pos++;
break;
}
pos++;
}
}
buf[buf_index++] = string[pos++];
}
where:
string is the C source code
buf a dynamic allocated string which expands as needed

Answer 3

It is very hard to do this perfectly without ending up writing a full C parser.
Consider the following, for example:
// Not using /*-style comment here.
// This line has an odd number of " characters.
while (1) {
printf("Wheee!
(*\/*)
\\// - I'm an ant!
");
/* This is a multiline comment with a // in, and
// an odd number of " characters. */
}
So, from the above, we can see that our problems include:
multiline quote sequences should be ignored within doublequotes. Unless those doublequotes are part of a comment.
single-line comment sequences can be contained in double-quoted strings, and in multiline strings.
Here's one possibility to address some of those issues, but far from perfect.
// Remove "-strings, //-comments and /*block-comments*/, then restore "-strings.
// Based on regex by mauke of Efnet's #regex.
$file = preg_replace('{("[^"]*")|//[^\n]*|(/\*.*?\*/)}s', '\1', $file);

Answer 4

try this:
$string = preg_replace("#\/\*\n?(.*)\*\/\n?#ms", "", $string);
Use # as regexp boundaries; change that u modifier with the right ones: m (PCRE_MULTILINE) and s (PCRE_DOTALL).
Reference: http://php.net/manual/en/reference.pcre.pattern.modifiers.php
It is important to note that my regexp does not find more than one "comment block"... Use of "dot match all" is generally not a good idea.