C ++ Using member functions from a similar virtual public class

Question

Suppose I have a bunch of inherited classes:

... and they all serve the purpose of creating all kinds of polynomials. A class Xis mainly a variable tank, classes A, Betc. - each virtual public Xand every one of them creates a type of the ont polynomial, the class Ymakes calls. In addition to Aand B, you can add any other class.

Now everything works, but for the newly added “virtual public” class, I need to reuse some member functions from other classes, here from Ainside the class B. I tried to make a simple example:

#include <iostream>
#include <cmath>
#include <functional>

// variable tank
class X
{
protected:
    // general variables
    double *m_c;
    int m_n;
    double m_w;
    // funcX related
    double m_r;
    int m_i {0};

public:
    ~X() = default;

    /* Simple bracketed root-finding. This is called from more than
     * one "virtual public" classes.
     */
    const double funcX(const double &x, const double &y,    \
                       std::function<const double(const double&, const int&)> fp,   \
                       const int &k)
    {
        double a {x}, b {y}, fmid;
        while (m_i<100)
        {
            m_r = 0.5*(a + b);
            fmid = fp(m_r, k);
            if (fabs(b-a) <= 1e-3)
                break;
            if (fmid < 0)
                b = m_r;
            else
                a = m_r;
            ++m_i;
        }
        return m_r;
    }
};

// one of the many classes that generate polynomials
class A: virtual public X
{
public:

    void funcA(const int &n)
    {
        // set order
        m_n = n;
        // calculate X::m_c[i]
        m_c = new double[m_n+1];
        for (short i=0; i<=m_n>>1; ++i)
        {
            int sgn {i%2 ? -1 : 1};
            m_c[i<<1] = sgn/((i + 1.0)*(i + 1.0));
        }
        // The polynomial is zero somewhere, use funcX() to find where.
        m_w = funcX(5.0, 0.0,   \
                    [this](const double &x, const int &n)   \
                    { return calcA(x, n); },    \
                    m_n);
    }

    // calculates the value of the polynomial of order n, at x
    const double calcA(const double &x, const int &n) const
    {
        double out {static_cast<double>(m_c[0])};
        for (short i=1; i<=n; ++i)
            out = m_c[i] + x*out;
        return out;
    }
};

class B: virtual public X
{
private:
    A m_a;  // otherwise the lambda function does not "catch" it
public:
    void funcB(const int &n)
    {
        // same as in A
        m_n = n;
        // same as in A, calculate coefficients
        m_c = new double[m_n+1];
        for (short i=0; i<=m_n; ++i)
        {
            int sgn {i%2 ? -1 : 1};
            m_c[i] = sgn/((i + 1)<<1);
        }
        /* Here I need A::calcA(). Instead of duplicating the code,
         * I want to call it through X::funcX(). The code compiles,
         * but it crashes.
         */
        m_w = funcX(0.5, 1.0,   \
                    [this](const double &x, const int &n)   \
                    { return m_a.calcA(x, n); },    \
                    m_n);
    }
    const double getW() const { return m_w; }
};

class Y: public A, public B
{
public:
    Y(const int &n, const int &i)
    {
        // call one of the "virtual public" classes through i
        switch (i)
        {
        case 1: funcA(n);    break;
        case 2: funcB(n);    break;
        }
    }
    void printC() { for (short i=0; i<=m_n; ++i) std::cout << m_c[i] << '\n'; }
    void printW() { std::cout << m_w << '\n'; }
    void printA(const double &x, const double &n) { std::cout << A::calcA(x, n) << '\n'; }
};

int main(int argc, char *argv[])
{
    int N {6};
    Y *y;
    for (short i=1; i<=2; ++i)
    {
        y = new Y(N, i);
        y->printC();
        y->printW();
        y->printA(1.2, N);
    }

    return 0;
}

class X:

X::funcX() - , virtual public (A, B ..). m_c, m_n, m_w .

classes A B:

funcA() ( funcB() ..) ( , for), , X::m_n. A::calcA(). class B, . - . "" ...

class Y

virtual public i (switch/case).

, . . A::funcA() , , m_c[i] , m_c[0] . new double[] insode A, .

, . , ? , ?

---

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Answer 1

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