Upcasting and identifying objects by address

This is a discussion on Upcasting and identifying objects by address within the C++ Programming forums, part of the General Programming Boards category; Up until now I always thought that you can identify an object by it's address in memory. This doesn't hold ...

  1. #1
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    Upcasting and identifying objects by address

    Up until now I always thought that you can identify an object by it's address in memory. This doesn't hold for upcasted pointers to different base classes when using multiple inheritance. These pointers can have different addresses than the address of the derived object and seeing how MI works, I can understand why this is.

    But now I've read that you can get differing addresses even in a single inhertance chain. So if you do:

    Derived* dp = new Derived;
    Base* bp = derived;

    you have no guarantee that these pointers hold the same address, even when it's not MI. Is that correct?

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    Any ideas?

  3. #3
    semi-colon generator ChaosEngine's Avatar
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    Quote Originally Posted by New++
    Derived* dp = new Derived;
    Base* bp = derived;

    you have no guarantee that these pointers hold the same address, even when it's not MI. Is that correct?
    that code won't even compile.

    but something like
    Code:
    Derived* dp = new Derived;
    Base* bp = dp;
    should mean that bp and dp have the same value
    "I saw a sign that said 'Drink Canada Dry', so I started"
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    Cough, well it was late when I wrote that.
    I also think that the address should be the same in such a case. Do you happen to know if this is guaranteed by the standard?

  5. #5
    semi-colon generator ChaosEngine's Avatar
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    I don't have a copy of the standard with me so I can't check, but I'd be extremely surprised if this was not the case.
    "I saw a sign that said 'Drink Canada Dry', so I started"
    -- Brendan Behan

    Free Compiler: Visual C++ 2005 Express
    If you program in C++, you need Boost. You should also know how to use the Standard Library (STL). Want to make games? After reading this, I don't like WxWidgets anymore. Want to add some scripting to your App?

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