using objects and pointers

This is a discussion on using objects and pointers within the C++ Programming forums, part of the General Programming Boards category; Hello, I am re-engineering someone elses code and have come across some code I don't really understand. To keep it ...

  1. #1
    UK2
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    using objects and pointers

    Hello,

    I am re-engineering someone elses code and have come across some code I don't really understand.

    To keep it simple I have just displayed the code snippets.

    I have a class called Board
    Code:
    class Board
    {
    	private:
    	Board *_boards[10];
    
    	public:
    	Board* const* boards() const; 
    .
    .
    .
    };
    
    Board* const* Board::boards() const
    {
    	return _boards;
    }
    Now I have another a cpp file that using this class.
    I have this code which I find hard to understand.
    Code:
    Board *board = static_cast<Board*>(boards()[i]);
    I don't know why there is a [i] at the end of the boards() function?

    Any advice would be most gratefull,

    Thanks,

  2. #2
    C++ Witch laserlight's Avatar
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    Quote Originally Posted by steve1_rm
    I don't know why there is a [i] at the end of the boards() function?
    It is another way of writing:
    Code:
    Board *board = static_cast<Board*>(*(boards() + i));
    That said, the static_cast looks unnecessary since you are copying a pointer that is const.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
    I get maybe two dozen requests for help with some sort of programming or design problem every day. Most have more sense than to send me hundreds of lines of code. If they do, I ask them to find the smallest example that exhibits the problem and send me that. Mostly, they then find the error themselves. "Finding the smallest program that demonstrates the error" is a powerful debugging tool.
    Look up a C++ Reference and learn How To Ask Questions The Smart Way

  3. #3
    UK2
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    Hello,

    Thanks for the response.

    So that this is really doing is:
    Code:
    (*boards()  + i))
    dereferencing and returning the board pointer object?

    However, just one more question.

    I have a member of that class. Called _boardID which is public. However, should be private for for testing purposes I have it as public.

    But I can't seem to access using the index:
    Code:
    board[0]._boardID = 1001;
    However, I can do this:
    Code:
    board->_boardID = 1001;
    I thought I should be able to access using both methods. However, the first one is needed as I need direct access to some elements.

    Any thoughts about this?

    Many thanks,

  4. #4
    Kernel hacker
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    I would also be a bit suspicious as to the correctness in a design where a member variable is a pointer to an array of the same class - doesn't seem quite right.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  5. #5
    UK2
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    Hello,

    Thanks for your input.

    Can you please explain your comment. I not sure I fully understand.

    Many thanks,

  6. #6
    Kernel hacker
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    Well, it is (most of the time) not quite right to have a pointer to the own object type. Exceptions would be for linked lists and trees of various kinds. But I don't thihk that is what you are doing?

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

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