Stripping off C/C++ comments from a source file using python

Question

I have a regular expression that ignores multiline comments that begin with /* ... */ But doesnt work with lines that begin with //

Can some one suggest what to add in this regex to make it ignore

pattern = r"""
                        ##  --------- COMMENT ---------
       /\*              ##  Start of /* ... */ comment
       [^*]*\*+         ##  Non-* followed by 1-or-more *'s
       (                ##
         [^/*][^*]*\*+  ##
       )*               ##  0-or-more things which don't start with /
                        ##    but do end with '*'
       /                ##  End of /* ... */ comment
     |                  ##  -OR-  various things which aren't comments:
       (                ## 
                        ##  ------ " ... " STRING ------
         "              ##  Start of " ... " string
         (              ##
           \\.          ##  Escaped char
         |              ##  -OR-
           [^"\\]       ##  Non "\ characters
         )*             ##
         "              ##  End of " ... " string
       |                ##  -OR-
                        ##
                        ##  ------ ' ... ' STRING ------
         '              ##  Start of ' ... ' string
         (              ##
           \\.          ##  Escaped char
         |              ##  -OR-
           [^'\\]       ##  Non '\ characters
         )*             ##
         '              ##  End of ' ... ' string
       |                ##  -OR-
                        ##
                        ##  ------ ANYTHING ELSE -------
         .              ##  Anything other char
         [^/"'\\]*      ##  Chars which doesn't start a comment, string
       )                ##    or escape
    """

At that point you may stop using regex only (multiline comments are not context free grammars anyway). I did use a custom parser to look for raw strings in C/C++ source files : github.com/lucasg/MSVCUnicodeUpdater/blob/master/sed.py — lucasg
– lucasg, Commented Aug 5, 2015 at 18:28
Looks like this is a case where going with a parsing framework such as pyparsing might be a lot more manageable. — shuttle87
– shuttle87, Commented Aug 5, 2015 at 18:29
HI @MichaelSPriz . I am writing a python tool that strips off comments (which contain perforce header information and date and time modified information) between two c/cpp files so that i could compare them and see if there is change in code. — Dennis Ninj
– Dennis Ninj, Commented Aug 5, 2015 at 18:29

Wiktor Stribiżew · Accepted Answer · 2015-08-05 22:39:09Z

1

If you plan using the current regexp, here is what you can do to match //... comments:

Below this:

 /                ##  End of /* ... */ comment

Add this:

 |                  ## OR it is a line comment with //
  \s*//.*           ## Single line comment

See demo

answered Aug 5, 2015 at 22:39

Wiktor Stribiżew

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