From: Rod Knowlton <rod.knowlton@...>
Date: 2006-09-14T08:38:12+09:00
Subject: Re: Regular expression question.


On Sep 13, 2006, at 10:55 AM, L7 wrote:

> In trying to parse a C source file I have the following section of
> code:
>
>    ...
>    ...
> case line
> when /^.*\/\*.*?\*\/.*$/       # single line comment(s)
>    non_comments = line.split(/\/\*.*?\*\//).to_s
>    process_code(non_comments)
> when /^.*\/\*\*?[^(\*\/)]*$/   # multi-line start
>    comment = true
>    next
> when /^[^(\/\*)]*\*\/.*$/      # multi-line end
>    comment = false
>    ...
>    ...
>



> Is there a way to look for the pattern '*/' without having a single  
> '*'
> break the search?

If I'm not mistaken, what you need is a negative lookahead

try   /^.*\/\*([^\/]|\/(?!\*))*$/  for multi-line start

and /^([^\*]|\*(?!\/))*\*\/.*$/ for multi-line end

the key difference (from the start pattern) is ([^\/]|\/(?!\*))

this breaks down like so:

(
[^\/]		# anything but /
|		# or
\/(?!\*)	# a / not followed by an * (don't eat the character after /,  
just peek at it)
)	

The pattern for multi-line end uses the same technique, but with the  
characters reversed.

I'm sure this isn't the be all and end all of C comment matching  
regexs, but it handles all of the cases you described.

- Rod