Linker chokes on virtual methods

[kahahn]

I don't know if this is a Qt issue, or that I'm not chaining my virtual types correctly. I am getting the same thing on a number of virtual functions. Below is an example.

I have

class entity_ao {
   public:
 
  ...
 
     virtual void setToZero();
 
  ...
}
 
class scalar_ao : public entity_ao {
  ...   
}
 
class real_ao : public scalar_ao {
   public:
 
   ...
 
   void setToZero() { ... }
 
   ...
}

class entity_ao {
   public:

  ...

     virtual void setToZero();

  ...
}

class scalar_ao : public entity_ao {
  ...   
}

class real_ao : public scalar_ao {
   public:

   ...

   void setToZero() { ... }

   ...
}

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This compiles just fine, but the .NET 2003 linker says: LNK2001: unresolved external symbol public: virtual void __thiscall entity_ao::setToZero(void)

I have tried adding virtual void setToZero(); to class scalar_ao, but that changes nothing. I have also tried moving the defn forreal_ao::setToZero from the .h to a .cpp file -- again that changes nothing.

[kahahn]

Ignore my post on this subject. I just figured out that the base class needs an instantiation of the virtual function. Doing that gets rid of the linker errors.

K.

[wysota]

You can also make the method pure virtual in the base class:

class entity_ao {
   public:
 
  ...
 
     virtual void setToZero() = 0;
 
  ...
}

class entity_ao {
   public:
 
  ...
 
     virtual void setToZero() = 0;
 
  ...
}

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The linker won't complain then.