C++ compile problem

This is a discussion on C++ compile problem within the C++ Programming forums, part of the General Programming Boards category; I have a compile problem here. I have a vector declared as: Code: std::vector<CGameObject> _vGameObjects; CGameObject is an abstract class. ...

  1. #1
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    Question C++ compile problem

    I have a compile problem here.
    I have a vector declared as:

    Code:
    std::vector<CGameObject> _vGameObjects;
    CGameObject is an abstract class.

    Code:
    _vGameObjects.push_back(_paddle);
    In the code above I want to push a _paddle object, which is an instance of a concrete object derived from the CGameObject.
    The compiler (VC++ 6.0) generates an error and a series of warnings:

    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : error C2259: 'CGameObject' : cannot instantiate abstract class due to following members:
    f:\projects\simple game\game1\src\cgameobject.h(33) : see declaration of 'CGameObject'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled
    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : warning C4259: 'void __thiscall CGameObject::InitBoundingBoxes(void)' : pure virtual function was not defined
    f:\projects\simple game\game1\src\cgameobject.h(51) : see declaration of 'InitBoundingBoxes'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled
    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : warning C4259: 'class std::vector<struct BBox,class std::allocator<struct BBox> > &__thiscall CGameObject::BoundingBoxes(void)' : pure virtual function was not defined
    f:\projects\simple game\game1\src\cgameobject.h(59) : see declaration of 'BoundingBoxes'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled
    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : error C2259: 'CGameObject' : cannot instantiate abstract class due to following members:
    f:\projects\simple game\game1\src\cgameobject.h(33) : see declaration of 'CGameObject'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled
    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : warning C4259: 'void __thiscall CGameObject::InitBoundingBoxes(void)' : pure virtual function was not defined
    f:\projects\simple game\game1\src\cgameobject.h(51) : see declaration of 'InitBoundingBoxes'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled
    c:\program files\microsoft visual studio\vc98\include\xmemory(34) : warning C4259: 'class std::vector<struct BBox,class std::allocator<struct BBox> > &__thiscall CGameObject::BoundingBoxes(void)' : pure virtual function was not defined
    f:\projects\simple game\game1\src\cgameobject.h(59) : see declaration of 'BoundingBoxes'
    c:\program files\microsoft visual studio\vc98\include\xmemory(66) : see reference to function template instantiation 'void __cdecl std::_Construct(class CGameObject *,const class CGameObject &)' being compiled


    Any suggestions? Thanks!

  2. #2
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    Make sure you define all your abstract methods somewhere, and you could use a vector of pointers to CGameObject rather than the objects themeselves as the vector implementation is probably trying to call the abstract constructor.

  3. #3
    Seeking motivation... endo's Avatar
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    You cannot create an abstract calss object. Use pointers as Sorensen suggested

    std::vector<CGameObject*> _vGameObjects;

    _vGameObjects->push_back(_paddle);

  4. #4
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    Thanks to both of you!

    I was wondering if I could use references instead of pointers. Is there any significative difference?

    ... on a second thought, it does not compile if I try using references... the pointer solution just works
    Last edited by Rhuantavan; 06-15-2002 at 03:34 PM.

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