RegEx - comments should not matches

[Chief of Chaos]

Fellow monks,

I would be very glad, if you can share your wisdom with me.

I try to find a regex which matches not out-commented lines.
Comments are '//' and '/* ... */'.
E.g.:

doApply()      <== match
// doNotApply()<== NOT match
/*
  doWhatEver() <== NOT match
*/

Thanks,
CoC

[Corion]

Weeding out comments is not as easy as you might think:

println( "This starts a comment? // Or does it\n" ); <== match ?

// /*
print( "*/ What happens now ?\n" ); <== match ??

You will need a parser for your language that understands the basics of that language at least well enough to know when the "comment starter markers" are within a string and when they actually apply. There is Text::Balanced and Regexp::Common, which have prefabricated regexes that attempt this task, and if they are not suitable for the language you are trying to parse, Parse::RecDescent or Parse::YAPP can be used to write your own parser.

[Chief of Chaos]

Thanks,
i will try Text::Balanced and Regexp::Common.

Sounds good :


Regexp::Common::comment
    Provides regexes for comments of various languages (43 languages c
+urrently).


Greetings,
CoC

[hardburn]

Regexp::Common::comment doesn't do proper tokenizing. IIRC, it will not catch the cases you presented correctly. I remember seeing a regex for catching C-style comments correctly (don't remember where, sorry), and it's quite ugly (but not as bad as the e-mail address regex).

[tomhukins]

You might find the replies to Help With Parsing and Commenting helpful.

[Happy-the-monk]

$string !~ m{^/[*/]}; # ^-beginning of the line, /- a slash [*/]-character class containing * and /

See   perldoc perlre.

Update:   !~   negates the match.

Update2: Thanks to Corion who pointed out that my approach didn't catch multiple line comments.

# a loop could do it like this:


$block_comment = 0;
while ( <INPUT> ) {
    if    ( m{^//}  ) { next; }
    elsif ( m{^/\*} ) { $block_comment = 1; next; } # start block
    elsif ( m{^\*/} ) { $block_comment = 0; next; } # end block
    elsif ( $block_comment) { next; } # inside block
    else { ... do something with the line, that is no comment ... }
}

Cheers, Sören

[Chief of Chaos]

Hi,
if I process this, it would not match the
commented line with doWhatEver().
But thanks.
CoC


#!/usr/local/bin/perl -w

while (<DATA>) {
 if ( $_ !~ m{^/[*/]} ) {
   print $_;
 }
}

__DATA__
doApply()

// doNotApply()

/*
  doWhatEver()
*/

Test4()


will show :


huxl:~>./tst.pl 
doApply()


  doWhatEver()
*/

Test4()

[danielcid]

It looks like you are trying to read a C/C++ file.
Be carefull that you can have "doApply() // comment" in
the same line. I wrote a little example for you, that
will only ignore the line if the comment is in the
beginning of the line or after tabs/spaces.

#!/usr/bin/perl

use strict;
use warnings;

if(!@ARGV)
        {
        die "program file.c\n";
        }

open(FILE,"<$ARGV[0]")|| die "Impossible to open $ARGV[0]\n";

my $ig=0;
while(<FILE>)
        {
        if($_ =~ /\*\//)
                {
                $ig=0;
                next;
                }
        next if(($_ =~ /(^\s+|^\t+|^)\/\//)||($_ =~ /(^\s+|^\t+|^)\/\*
+.+\*\//));
        $ig=1 if($_ =~ /\/\*/);
        next if($ig == 1);
        print "$_";
        }
exit;



-DBC