Question

So I have a base class with the following header file:

#ifndef ODESolver_H
#define ODESolver_H
#endif
#include "DoublePendulum.h"

class ODESolver
{
public: 
    ODESolver(DoublePendulum &);
    virtual void Predict(const double &)=0;
    DoublePendulum DP;
};

Implementation:

#include "ODESolver.h"
#include <iomanip>

ODESolver::ODESolver(DoublePendulum &DPRef) :DP(DPRef)
{}

And a class that inherits from it:

#ifndef ODEEuler_H
#define ODEEuler_H
#endif

#include "ODESolver.h"

class ODEEuler : public ODESolver
{
public:
    ODEEuler(DoublePendulum &);
    void Predict(const double &);
};

Implementation:

#include "ODEEuler.h"

ODEEuler::ODEEuler (DoublePendulum &DPRef) :ODESolver(DPRef)
{}

void ODEEuler::Predict(const double &dt=0.005)
{
    DP=DP+DP.Derivate()*dt;
    cout << DP.getUp().getTheta() << endl;
}

The problem is that in the above implementation, DP=DP+DP.Derivate()*dt; won’t do anything. I have no clue how this is possible. I have checked if the .Derivate() member function works and it actually returns the correct values/object. On top of that, it doesn’t matter what I do there e.g. DP=DoublePendulum RandomObject(1,2,3,4) will still keep DP the same. Any ideas? I hope I provided enough information…

Also the implementation and declaration of DoublePendulum etc:

http://pastebin.com/ny3pU8aR

Answer 1

This assignment operator

DoublePendulum DoublePendulum::operator= (DoublePendulum &DoublePendulumA)
{
        return DoublePendulum (DoublePendulumA);
}

creates a new value, but does not really assign anyting to the left-hand-side of the assignment. That’s why it doesn’t change!

The standard form of assignment looks like

DoublePendulum& DoublePendulum::operator= (const DoublePendulum& DoublePendulumA)
{
    // assign to members of this object

    return *this;
}