Polymorphism exercise error message
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Hi all
I have an abstract base class Shape and three classes that derive from it Line Circle and rectangle. when I try to instantiate any class that derive from "Shape" I get an error message saying e.g undefined reference to vtable for Circle. I tried cleaning and rebuilding and running cmake again but still no change. Any idea why this is happening?
my code:
Shape.h
@
#ifndef SHAPE_H
#define SHAPE_H
#include <QString>class Shape
{
public:
virtual QString getType();
virtual double getArea() = 0;
virtual QString toString() = 0;
protected:
QString type;
};#endif // SHAPE_H
@Circle.h
@
#ifndef CIRCLE_H
#define CIRCLE_H
#include <QString>
#include "Shape.h"
#include "Point.h"class Circle : public Shape
{
public:
Circle(Point c, double r);
double getArea();
QString toString();
private:
Point center;
double radius;
};#endif // CIRCLE_H
@Circle.cpp
@
#include "Circle.h"
#include <math.h>
#include <QString>Circle::Circle(Point c, double r) : center(c), radius(r) {
}double Circle::getArea() {
return M_PI * (radius * radius);
}QString Circle::toString() {
return QString("Center: %1 \n Radius: %2").arg(center.toString()).arg(radius);
}
@main.cpp
@
#include <QString>
#include "Line.h"
#include "Point.h"
#include "Shape.h"
#include "Circle.h"
#include "Rectangle.h"
#include "ShapeList.h"
#include <QTextStream>QTextStream cout(stdout);
int main() {
ShapeList list;
Point p1(0, 0);
Point p2(-1, 0);
Point p3(0, 1);
Point p4(1, 1);Circle circle(p1, 1);
Line line(p1, p2);
Rectangle rectangle(p4, 3, 1);Shape* s1 = &circle;
Shape* s2 = &line;
Shape* s3 = &rectangle;list.append(s1);
list.append(s2);
list.append(s3);cout << "area of Circle with center (0,0) and radius 1 is " << s1->getArea() << endl;
cout << "Area of any line is " << s2->getArea() << endl;
cout << "Afea of rectangle with top lef corner (1, 1) and which also contains the point (3, 1) is " << s3->getArea() << endl;
return 0;
}
@To make my post shorter I didn't include the Point Line Rectangle and ShapeList classes.
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Hi,
Strange thing I can see: getType has no implementation.
On a side note, none of your getter are constant
and
@
Shape* s1 = &circle;
Shape* s2 = &line;
Shape* s3 = &rectangle;list.append(s1);
list.append(s2);
list.append(s3);
@Is a bad Idea, you are taking the address of temporary variables. While this will work in this precise case, it's recipe for disaster later.
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Thanks SGaist would it be better to add it to this list in this way: list.append(&circle)?
I iplimented getType() and most of the errors disappeared.. The only one still there is undefined reference to vtable for Line... Any idea what that means?my code for Line:
Line.h
@
#ifndef LINE_H
#define LINE_H
#include <QString>
#include "Shape.h"
#include "Point.h"class Line : public Shape {
public:
Line(Point p1, Point p2);
double getArea();
QString toString();
private:
Point oneEnd;
Point otherEnd;
};#endif // LINE_H
@Line.cpp
@#include "Line.h"Line::Line(Point p1, Point p2) : oneEnd(p1), otherEnd(p2) {
type = QString("Line");
}double getArea() {
return 0;
}QString Line::toString() {
return QString("%1 %2").arg(oneEnd.toString()).arg(otherEnd.toString());
}
@my getType returns the type sent by it when any shape is initialized.
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No it would not since it's basically the same action but only on one line. You are still taking the address of a temporary. Either use a QList<Shape> or allocate your shapes on the heap. Since you have a pretty simple class you should rather go for QList<Shape>.
Was Shape a QObject and you removed the Q_OBJECT macro ? If so, re-run qmake before building again.
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Compare all their implementations and see where you did something differently for Line
