Question about autro_ptr

This is a discussion on Question about autro_ptr within the C++ Programming forums, part of the General Programming Boards category; Hello, I am using auto_ptr for the first time in a large project, but I have a question. How does ...

  1. #1
    Registered User Mortissus's Avatar
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    Question about autro_ptr

    Hello, I am using auto_ptr for the first time in a large project, but I have a question. How does an auto_ptr knows when to use delete[] or delete? I am using in like this:

    Code:
    auto_ptr<char> buffer(new char[buff_size]);
    In this case, auto_ptr should delete de pointer with delete[].

    What about:

    Code:
    auto_ptr<AnObject> buffer(new AnObject);
    Thanks any insight.

  2. #2
    C++ Witch laserlight's Avatar
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    From what I understand, auto_ptr stores a pointer to an object obtained via new, not new[].
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    Registered User Mortissus's Avatar
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    Would not make it almost useless?

  4. #4
    C++ Witch laserlight's Avatar
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    Would not make it almost useless?
    No, since it can still be used to perform RAII with a single object, after all.

    Note that what you are trying to do by using auto_ptr with new[] can be accomplished with say:
    Code:
    std::vector<char> buffer(buff_size);
    Last edited by laserlight; 07-02-2007 at 09:00 AM.
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    Registered User Mortissus's Avatar
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    Well, if I am going to use a vector, using a pointer is no longer interesting, since I do not need dynamic allocation anymore.

    Thanks for the help.

    Edit: I forgot to ask. Can I really do something like:

    Code:
    vector<char> buff;
    
    // populate vector
    
    send(sock_fd, &buff[0], buff.size(); // send through socket connection
    Is it really safe and portable??
    Last edited by Mortissus; 07-02-2007 at 10:25 AM.

  6. #6
    C++ Witch laserlight's Avatar
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    Is it really safe and portable??
    As far as I know, yes, at least where &buff[0] is concerned.
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  7. #7
    Frequently Quite Prolix dwks's Avatar
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    The memory allocated for a vector is guaranteed to be contiguous. http://www.thescripts.com/forum/thread141366.html

    So I think that if you added an extra ')', that code would work just fine.
    dwk

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    Registered User Mortissus's Avatar
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    Ok! Thanks!

  9. #9
    Algorithm Dissector iMalc's Avatar
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    The following from ATL could be useful:
    Code:
    CAutoVectorPtr
    CAutoPtr
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  10. #10
    Cat without Hat CornedBee's Avatar
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    ATL is a big (and platform-specific) dependency to pull in for mere containers.

    Try Boost.PtrContainer instead.
    All the buzzt!
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  11. #11
    Registered User Mortissus's Avatar
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    I do not know ATL, is it like Boost?
    Installing Boost would not worth it, since I would only need the auto_ptr functionality.

  12. #12
    Absent Minded Programmer
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    Boost is SOOOO useful when it comes to sweet pointer objects and lots of other nifty stuff, I use it for serialization too.

    I'd suggest using it as much as possible, it's one of the best libraries out there I think
    Sometimes I forget what I am doing when I enter a room, actually, quite often.

  13. #13
    Registered User Mortissus's Avatar
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    Then I shall take a look, thank you.

  14. #14
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    In addition, for most of the boost libraries you don't even have to build it. Just download and set your include path to the boost_1_34 (or whatever it is) directory and you can use the ptr_vector.

    Although in this case there's no need for the boost libraries, vector<char> is exactly what you want. The vector class does for arrays what auto_ptr does for regular pointers (auto_ptr has some weird differences, but basically this is correct).

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