references and multiple inheritance - incompatible?

This is a discussion on references and multiple inheritance - incompatible? within the C++ Programming forums, part of the General Programming Boards category; is it possible to use a class with reference type members? it seems not since classes using multiple inheritance must ...

  1. #1
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    references and multiple inheritance - incompatible?

    is it possible to use a class with reference type members? it seems not since classes using multiple inheritance must have a default constructor, which leaves the references uninitialized, or at best incorrectly initialized.

    if there's a way, someone please show how!

  2. #2
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    What is the reference supposed to point to?
    If that's not working, why not use a pointer instead?

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    C++ Witch laserlight's Avatar
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    Are you sure that "classes using multiple inheritance must have a default constructor"? Methinks that the derived class ctor can initialise the base class subobjects via its initialisation list. Of course, even if what you say is true, there is no reason that classes with reference members must be part of a multiple inheritance hierarchy.
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    Quote Originally Posted by laserlight
    Methinks that the derived class ctor can initialise the base class subobjects via its initialisation list.
    ah-ha...i will try this.


    i am just asking; i haven't actually encountered such a need to use references in a multiply derived object.

    i had an unneeded virtual keyword in a class definition. when i went to derive it, i ran across this problem and i didn't see any immediate way around it other than to nix the virtual keyword (which i should have anyway i suppose).

    thanks for the comments. i'll try that if i need to. i was just curious if there was an obvious solution i was overlooking, and it appears that was probably the case.

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    ok, i looked more closely and it still does not compile if the derived ctor initializes the reference of the base class.

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    C++ Witch laserlight's Avatar
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    Show your code.
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    Code:
    __fastcall analysisModule::analysisModule(process *owner,String mName,spectrometer &Sensor,int h,int w) :
            procObj(),
            onLoadEqnSet(taskArray(mName+" On Load New Eqn Set")),
            firstLoad(true),
            sensor(Sensor),
            applyData(false)
            {
    
                    init(owner,mName,h,w);
            }
    
    __fastcall analysisModule::analysisModule() :
            procObj(),
            onLoadEqnSet(taskArray("Analysis Module: On Load New Eqn Set")),
            firstLoad(true)
            {
    
            }
    sensor is not initialized in the default ctor

  8. #8
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    So, you probably want a pointer to Sensor rather than a reference to Sensor (or you want a "DummySensor" that you can set Sensor to in the case where you don't use a sensor).

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    yes, i used a pointer before in fact, but i have been trying to optimize where possible to use references instead of pointers.

    the case of virtual inheritance is the first time i have encountered a situation were they were not interchangeable.
    Last edited by m37h0d; 09-03-2008 at 10:25 AM.

  10. #10
    C++まいる!Cをこわせ! Elysia's Avatar
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    To the extent of my knowledge, a class can only initialize its own members via the initializer list.
    What you can do is create a constructor for the base class to initialize the reference and call this base class constructor via the initializer list instead.
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    Quote Originally Posted by m37h0d View Post
    yes, i used a pointer before in fact, but i have been trying to optimize where possible to use references instead of pointers.

    the case of virtual inheritance is the first time i have encountered a situation were they were not interchangeable.
    There is also no benefit between a reference or pointer with regards to performance. Under the hood [1] a reference becomes a pointer - the only difference is in the fact that a pointer can be assigned at any time, and syntactically it "looks different".



    [1] Except for a few instances where the compiler can figure out what the reference is actually referring to and "optimize away the whole reference variable alltogether".

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    yes, i meant optimization for safety more than speed, but i generally do a good job of making sure my pointers point to things (or are assigned NULL)

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