Abstract method inheritance

[space_otter]

I have two classes of the form:

class DNumber
{
    static int Digits;
    virtual DNumber* add(const DNumber* a, unsigned digits) const = 0;
    DNumber* add(const DNumber* a) const {return add(a, Digits);}
}
 
class DInteger : public DNumber
{
    // implementation uses runtime type checking to perform addition
    DInteger(int value);
    DNumber* add(const DNumber* a, unsigned digits) const;
}

class DNumber
{
    static int Digits;
    virtual DNumber* add(const DNumber* a, unsigned digits) const = 0;
    DNumber* add(const DNumber* a) const {return add(a, Digits);}
}

class DInteger : public DNumber
{
    // implementation uses runtime type checking to perform addition
    DInteger(int value);
    DNumber* add(const DNumber* a, unsigned digits) const;
}

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Attempting to use this:

DInteger* cien = new DInteger(100);
    DInteger* dos = cien->add(cien);
    qDebug() << dos->toString();
 
    delete cien, delete dos;

DInteger* cien = new DInteger(100);
    DInteger* dos = cien->add(cien);
    qDebug() << dos->toString();

    delete cien, delete dos;

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Results in a compile error:

error: no matching function for call to 'DInteger::add(DInteger*&)'

DInteger should inherit add(DNumber*) right?

[tbscope]

error: no matching function for call to 'DInteger::add(DInteger*&)'

Somewhere in your code you're adding a value and not a pointer.

[space_otter]

The error is from line 2 of the second box of code. cien is a pointer. Also, code completion thinks that add(DNumber*) does not exist for DInteger as well. But it inherits DNumber! Why? It must be the call to a pure virtual function--other methods are inherited properly. Is there any way to make this work?

#include <iostream>
 
int Digits = 20;
 
class A
{
	virtual A* f(const A* a, int b) const = 0;
	A* f(const A* a) const {return f(a, Digits);}
};
 
class B : public A
{
	A* f(const A* a, int b) const
	{
		std::cout << b;
		return new B();
	}
};
 
int main(int argc, char ** argv)
{
	B* foo= new B();
	B* bar= new B();
	B* r = foo->f(bar);
 
	delete foo, delete bar, delete r;
 
	return 0;
}

#include <iostream>

int Digits = 20;

class A
{
	virtual A* f(const A* a, int b) const = 0;
	A* f(const A* a) const {return f(a, Digits);}
};

class B : public A
{
	A* f(const A* a, int b) const
	{
		std::cout << b;
		return new B();
	}
};

int main(int argc, char ** argv)
{
	B* foo= new B();
	B* bar= new B();
	B* r = foo->f(bar);
	
	delete foo, delete bar, delete r;
	
	return 0;
}

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Same error. no match for B::f(B*&)

[tbscope]

You can not overload the function f in this way. All the A::f functions get hidden by the B::f function.
Either implement all the A::f functions in B too or rename A::f to A::f2

Example:

A* f2(const A* a) const {return f(a, Digits);}

A* f2(const A* a) const {return f(a, Digits);}

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Then do something like this:

A* r = foo->f2(bar);

A* r = foo->f2(bar);

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Edit:
Be careful with your class definitions.
Your functions are all private and you do not define any constructors. Note that the compiler will fill these in automatically, but it might not be what you want.