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Jonathan Browns · Guest

Dear comp.lang.c++.moderated,

Using MS Visual C++, I am trying to create two abstract classes, one
is a member of another, after that I am trying to use these classes as
base of two concrete clases.

Trying to use it in the following brief sample code give me a lot of
cannot "instantiate abstract class due to following members" errors.

---------- o ----------
class A {
public:
virtual void setNumber(int) const = 0;
virtual int getNumber() const = 0;
};

class B {
public:
virtual A myNumber() const = 0;
};

class C: public virtual A {
public:
virtual void setNumber(int a);
virtual int getNumber();
private:
int n;
};

void C::setNumber(int aNumber)
{
n = aNumber;
}

int C::getNumber()
{
return n;
}

class D: public virtual B {
public:
virtual C myNumber();
};

C D::myNumber()
{
C aNumber;

aNumber.setNumber(5);

return aNumber;
}

int main(int argc, char* argv[])
{
C number;
D d;

printf("%dn", d.myNumber().getNumber());

return 0;
}
---------- o ----------

It would very helpful if somebody can point me how to solve this maze.
My few experience is on dynamic typing languages.

The errors I receive were:

---------- o ----------
testcpp.cpp(15) : error C2259: 'A' : cannot instantiate abstract class
due to following members:
testcpp.cpp(7) : see declaration of 'A'
testcpp.cpp(15) : warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(15) : warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(3 Cool

: error C2259: 'C' : cannot instantiate abstract class
due to following members:
testcpp.cpp(1 Cool

: see declaration of 'C'
testcpp.cpp(3 Cool

: warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(3 Cool

: warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(42) : error C2259: 'C' : cannot instantiate abstract class
due to following members:
testcpp.cpp(1 Cool

: see declaration of 'C'
testcpp.cpp(42) : warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(42) : warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(43) : error C2259: 'C' : cannot instantiate abstract class
due to following members:
testcpp.cpp(1 Cool

: see declaration of 'C'
testcpp.cpp(43) : warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(43) : warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(43) : error C2259: 'C' : cannot instantiate abstract class
due to following members:
testcpp.cpp(1 Cool

: see declaration of 'C'
testcpp.cpp(43) : warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(43) : warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(52) : error C2259: 'C' : cannot instantiate abstract class
due to following members:
testcpp.cpp(1 Cool

: see declaration of 'C'
testcpp.cpp(52) : warning C4259: 'void __thiscall A::setNumber(int)
const' : pure virtual function was not defined
testcpp.cpp(9) : see declaration of 'setNumber'
testcpp.cpp(52) : warning C4259: 'int __thiscall A::getNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(10) : see declaration of 'getNumber'
testcpp.cpp(53) : error C2259: 'D' : cannot instantiate abstract class
due to following members:
testcpp.cpp(36) : see declaration of 'D'
testcpp.cpp(53) : warning C4259: 'class A __thiscall B::myNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(15) : see declaration of 'myNumber'
testcpp.cpp(53) : error C2259: 'D' : cannot instantiate abstract class
due to following members:
testcpp.cpp(36) : see declaration of 'D'
testcpp.cpp(53) : warning C4259: 'class A __thiscall B::myNumber(void)
const' : pure virtual function was not defined
testcpp.cpp(15) : see declaration of 'myNumber'
testcpp.cpp(55) : error C2264: 'myNumber' : error in function
definition or declaration; function not called
testcpp.cpp(55) : error C2228: left of '.getNumber' must have
class/struct/union type
---------- o ----------

Thank You All
Jonathan Browns

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Ulrich Eckhardt · Guest

Jonathan Browns wrote:

Ron · Guest