Nested comments don't work?

This is a discussion on Nested comments don't work? within the C++ Programming forums, part of the General Programming Boards category; I was wondering why multiline C-style comments don't work? Code: /* BEGIN_COMMENT1 /* BEGIN_COMMENT2 */ END_COMMENT2 */ END_COMMENT1 The reason ...

  1. #1
    Programming Ninja In-T...
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    Nested comments don't work?

    I was wondering why multiline C-style comments don't work?

    Code:
    /* BEGIN_COMMENT1
      /* BEGIN_COMMENT2
      */ END_COMMENT2
    */ END_COMMENT1
    The reason I'm asking is, I want to comment out some code in the constructor of my class using the multiline comments, but I had already written some multiline comments as description headers for different things inside the area I want to comment, so I can't just simply wrap it with the multiline comments, and be done with it, because that doesn't work. And its a pain to have to go through the whole function again just to change some comment styles (the function is some 70,000+ lines of code), so is there another way to do this??

    Thanks in advance.
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  2. #2
    Algorithm Dissector iMalc's Avatar
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    Nope they don't work in anything I've ever tried, and there are no plans to change that afaik.
    Just put a #if 0 #endif around the code you want to temporarily disable.
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  3. #3
    Been here, done that.
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    Since /* ... */ are C-style comment, you should be using the C++ style // comments for your code.

    Then when you want to comment out a section, the /* ... */ style will work much better.
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  4. #4
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    Quote Originally Posted by iMalc View Post
    Nope they don't work in anything I've ever tried, and there are no plans to change that afaik.
    Just put a #if 0 #endif around the code you want to temporarily disable.
    Well, I tried that already after reading about it on the web, but the example that they showed was around the function declaration, not inside of a function definition, which is where I need it.
    So I'm guessing that doing it inside a function definition is not legal, since doing that produced a whole mess of compiler errors... EDIT: Nevermind...maybe its legal, its just causing other problems.
    Quote Originally Posted by WaltP View Post
    Since /* ... */ are C-style comment, you should be using the C++ style // comments for your code.

    Then when you want to comment out a section, the /* ... */ style will work much better.
    Well, I'm actually using both. I used // above less-important sections of code, while /* and */ above more important or bigger sections of code, so that, for instance, I could differentiate the attributes code from the Html tags code, since attribute code is inside Html tag code, and each attribute is a separate entity within the tag. But, anyway, I suppose I could have used ///////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// in place of that instead, but I didn't know starting out that nesting multiline comments is not allowed.

    So now I guess I'll have to write a short little program to do the tedious task of changing comment styles for me, so I wont have to do it all by hand....
    Last edited by Programmer_P; 09-23-2012 at 03:22 PM.
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  5. #5
    Registered User whiteflags's Avatar
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    C comments don't nest. I am pretty sure it's in the grammar section of the standard, so you won't find a tool where this works.

    Not sure how you screwed up the #if 0 suggestion. Try below:

    So now I guess I'll have to write a short little program to do the tedious task of changing comment styles for me, so I wont have to do it all by hand....
    Not a terrible idea but: Surround the code you want to exclude in an #ifdef...#endif then define the macro when you want it again with a compiler switch or something.

  6. #6
    Captain Crash brewbuck's Avatar
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    Another way to "comment out" a section of code is to:

    Code:
    if (false)
    {
        // code that will not be executed
    }
    It's not exactly the same as commenting it out, because it'll still be parsed and syntax-checked, but in a pinch it works.

    To disable an if-statement, you can add "&& false" to the condition:

    Code:
    if (false && condition)
    {
        // disabled
    }
    The #if 0...#endif is pretty universal, though. If that didn't work for you, chances are your program doesn't operate correctly with that region of code removed.
    Code:
    //try
    //{
    	if (a) do { f( b); } while(1);
    	else   do { f(!b); } while(1);
    //}

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