Why i am not able to cast pointer to the class structure - c++

Question

I have a Geometry class
class Geometry
{
public:
std::string stdstrType;
bool bValid;
public:
Geometry()
Geometry( std::string strType , bool bValue )
Geometry(const Geometry &g)
~Geometry()
virtual void draw();
bool isValid();
void setValidState(bool bState);
virtual void Init();
std::string GetName();
};
Which is the base class for Geometry objects like in this case for Sphere class
class Sph : public Geometry
{
public:
Sph( float radius , float segments );
~Sph();
void init();
void CleanUp();
void draw();
private:
float fRadius, fSegments;
bool isInited;
unsigned int m_VAO, m_VBO;
int iNumsToDraw;
SumShader shader;
bool isChanged;
};
I have a Tree structure holding different Container objects and Geometry is a data type in the Container object.
class Container
{
private:
std::string stdstrContainerName;
std::string stdstrPluginType;
Geometry Geom;
}
Since each item in the tree can hold a circle sphere or rectangle so I would like to use the draw function of geometry to draw the Geometry object types.
For this when I try to cast any Geometry Object type to Geometry I get an error.
Sph sphere(0.1 , 32);
Geometry *geom = &sphere;
Container cont("Sphere" , "SPHERE" , *geometry );
myModel->SetContainer(child, cont);
The Constructor for Container
Container::Container( std::string strName, std::string strType, const
Geometry& geometry) : Geom(geometry)
{
stdstrContainerName = strName;
stdstrPluginType = strType;
}
void TreeModel::SetContainer(const QModelIndex &index, Container Cont)
{
TreeItem *item = getItem(index);
item->setContainer(Cont);
}
class TreeItem
{
public:
// Functions here
private:
QList<TreeItem*> childItems;
Container itemData;
TreeItem* parentItem;
};
1) Is this the correct approach?
2) How can I cast the Geometry objects to the Geometry pointer?

Answer 1

With
Sph sphere();
You have declared a function wich return a Sphere object and take no parameters.
To declare an object to Sph you just simple write
Sph sphere; or Sph sphere{};
I guess you tried the first but it didn't compile, so you just changed the signature "until compiled".
You have declared a custom constructor, which means the compiler does not provide you anymore a default constructor so you can't declare a variable without calling the correct constructor (and in your case it wouldn't have sense).
In addition with
Geometry *geom = new Geometry;
geom = &sphere;
you're creating a new pointer geometry than leaking it immediatly and reassigning to a sphere geometry which has no sense at all.
Moreover all your method are public in Geometry and this does not have sense (why putting bool valid public and then a getter?).
in addition class Container is holding an instance to a base class which will give you issues due to object slicing, you need to use a pointer or a reference.
for just answering to your question you should instance a sphere with
Geometr* geom = new Sphere(1, 5); // random numbers
but the most genuine and honest thing I can tell is to rewrite everything from scratch and before that to study a little more trying with an easier example.

Answer 2

The minimal code that works and implements an idea in the question:
#include <iostream>
class Geometry
{
public:
Geometry(const std::string type) { stdstrType = type; }
std::string GetName() { return stdstrType; }
virtual void draw() {} ;
private:
std::string stdstrType;
};
class Sphere : public Geometry
{
public:
Sphere(float radius): Geometry("Sphere ") { fRadius = radius; }
virtual void draw() { std::cout << GetName() << fRadius << "\n";}
private:
float fRadius;
};
class Container
{
public:
Container(std::string strName, Geometry* g)
{
stdstrContainerName = strName;
geometry = g;
}
void draw() { geometry->draw(); }
private:
std::string stdstrContainerName;
Geometry *geometry;
};
int main(int argc, const char * argv[]) {
Sphere sphere(0.1);
Geometry *geom = &sphere;
Container cont("Sphere container", geom);
cont.draw();
return 0;
}
Xcode 10.2.1: No Buildtime/Runtime Issues. Output:
Sphere 0.1
Program ended with exit code: 0