Multiline comments

Nature Boy

Here's something that I can't understand.

If I have some code (I'm using C#, but this is common to any C style language) like so:

              if (a == b)
Brace 1 ->    {
                  if (a == c)
Brace 2 ->        {
                      a = d;
Brace 3 ->        }
Brace 4 ->    }

Here, Brace 1 will be matched with Brace 4 and Brace 2 will be matched with Brace 3. Just as expected!

However, if I have:

Comment 1 ->    /*
                  if (a == c)
Comment 2 ->        /*
                      a = d;
Comment 3 ->        */
Comment 4 ->    */

Comment 1 will be matched with Comment 3, Comment 2 won't match with anything, and Comment 4 will cause a compiler error.

Why don't multiline comments work in the same way as braces and parentheses??? This annoys me when I'm debugging!!

aidan_walsh

Its because Comment 2 is a part of Comment 1 since it is enclosed in it.

Even if Comment 4 was above Comment 3, they would still be within the initial matching braces of Comment 1 and Comment 3, and so wouldn't actually need to be comment tags at all.

satchmo

Use #if 0 and #endif instead, they'll stack the way you want them to.

Khannie

This should be down to the compiler and its interpretation. The default interpretation is as aidan pointed out, and I quite like it that way personally.

The MS compiler has an option to behave as you expect (or at least, I'm pretty sure it did in VC++ 6.0).

nobodythere

A multiline comment is opened by /* and closed by */. There's no point in programming a comment inside a comment so it ignores the second /*

satchmo

Khannie wrote:

This should be down to the compiler and its interpretation.

According to the standard, /* */ comments don't nest so you shouldn't rely on a particular compiler's different interpretation for any sort of cross-platform code.

I quite like it that way personally

Yeah I like it the way it is too, it makes sense - you don't have to go hunting for matching close-comments the way you do with braces.

Capt'n Midnight

Nature Boy wrote:

[php]
if (a == b)
Brace 1 -> {
if (a == c)
Brace 2 -> {
a = d;
Brace 3 -> }
Brace 4 -> }
[/php]


[php]
Comment 1 -> /*
if (a == c)
Comment 2 -> /*
a = d;
Comment 3 -> */
Comment 4 -> */
[/php] !

php tags give some colour - but like the others have said the rules for continuing on the next line vary. If you use /* */ on each line it should always work - not so pretty unless you match the right hand side too.

Nature Boy

Thanks for the replies. The reason I'm asking is that if I've got code with a multiline comment somewhere and I want to comment out the entire block of code for debugging reasons, I have to take out all of the multiline comments and replace them with single lines, which can be a pain! Most other things can be nested, why not comments??

Capt'n Midnight

Aren't there compiler options you can use to get the compiler to miss sections ?

ReallyDeadThing

Nature Boy wrote:

if I've got code with a multiline comment somewhere and I want to comment out the entire block of code for debugging reasons, I have to take out all of the multiline comments and replace them with single lines, which can be a pain!

I find that annoying too. One handy solution I've started using is to replace the /* and */ in the inner comment with //. For example:

/*
  if (a == c)
    //
      a = d;
    //
*/

The // acts as a reminder to put the proper comment block back in once the whole thing is uncommented.