Thread: assignment constructor overloading

Originally Posted by laserlight

If this is with respect to my definitions of A and B in post #7, then it is as simple as:

Code:

printit(b2);

it doesn't work, it print's A print method

Originally Posted by -EquinoX-

it doesn't work, it print's A print method

You probably made the print member function non-virtual when adapting my example. Try this:

Code:

#include <ostream>

class A
{
public:
    virtual ~A() {}

    virtual void print(std::ostream& out) const
    {
        out << "A";
    }
};

class B : public A
{
public:
    explicit B(int x) : x(x) {}

    virtual void print(std::ostream& out) const
    {
        out << "B: " << x;
    }
private:
    int x;
};

#include <iostream>

void printit(const A& a)
{
    a.print(std::cout);
    std::cout << std::endl;
}

int main()
{
    A a;
    printit(a);

    B b(2);
    printit(b);
}

Originally Posted by -EquinoX-

maybe I am not a bit clear... I want it to print out using A's print but printing out B's value...

In that case, your design is simply wrong. B should not be derived from A. Rather, A and B should be separate, but you could have a B as a member of A:

Code:

#include <ostream>

class B
{
public:
    explicit B(int x) : x(x) {}

    int get() const
    {
        return x;
    }
private:
    int x;
};

class A
{
public:
    explicit A(const B& b) : b(b) {}

    virtual void print(std::ostream& out) const
    {
        out << "A: " << b.get();
    }
private:
    B b;
};

#include <iostream>

int main()
{
    A a(B(2));
    a.print(std::cout);
    std::cout << std::endl;
}

Originally Posted by -EquinoX-

no I am pretty sure that B has to be derived from A

If you are sure that B has to be derived from A, then you are sure that A should have at least one virtual function. As such, why can you not use a virtual print function?

I did use print as a virtual function.. it did not work though.. here's my code:

2shared - download code.txt

in the code when calling printit(b2) it did call A's print, which is "funds blah..blah (which is right)" but then the value is wrong.. (it's 0 instead of 2, while b2's value is 2) that's my only problem

Originally Posted by -EquinoX-

I did use print as a virtual function.. it did not work though..

What did you try?

Originally Posted by -EquinoX-

in the code when calling printit(b2) it did call A's print, which is "funds blah..blah (which is right)" but then the value is wrong.. (it's 0 instead of 2, while b2's value is 2) that's my only problem

Post the smallest and simplest compilable code that demonstrates the problem. If you really cannot post that, then post your code here, using the file attachment feature if necessary. Frankly, it took me too long to figure out how to download from 2shared, so I cannot be bothered.

You need to post hw06-question2.h as well.

You did not declare A's print member function as virtual.

If I do a's print as virtual it would print funds withdrawn instead of funds deposited.... I want it to print funds deposited... and when I do b2.print I want it to print funds withdrawn...
It's so complicated

Originally Posted by -EquinoX-

I did try all possibilites of virtual and it still doesn't print b2's value as 2

I think that it is likely that you still have a type slicing problem. Another potential problem is that you have a public member variable named value in B. This hides the value member variable inherited from A.

I do not understand why you need to use inheritance, but this is my remedy for your type slicing problem: turn A into an abstract base class, e.g., declare its print member function as pure virtual, or declare its destructor as pure virtual (but keep the implementation of A's destructor).

Originally Posted by laserlight

I think that it is likely that you still have a type slicing problem. Another potential problem is that you have a public member variable named value in B. This hides the value member variable inherited from A.

I do not understand why you need to use inheritance, but this is my remedy for your type slicing problem: turn A into an abstract base class, e.g., declare its print member function as pure virtual, or declare its destructor as pure virtual (but keep the implementation of A's destructor).

so I don't need an implementation of A? and I can't do A a; ?