Elements of constructor get deleted by call from another class
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I am defining an array with all its elements in the constructor of one class A. Now I want to use these values in my other class B.
I am defining an Object A *a = new A() and call the array with a->array Unfortunately all the elements are deleted as soon as I am leaving the constructor from class A. Has anyone an idea why that is so?
Here an update with a sample-code:
First I have my class A:
@
class A()
{
QVector<Point3d> point_s;
}A::A()
{
point_s.resize(5);
for (int i = 0; i < 5; ++i)
{
point_s[i].x = i;
point_s[i].y = i+1;
point_s[i].z = i+2;
}
}
@
In class B I want to use the array-values. I am creating an Object from A.
@
#include "a.h"
#include "c.h"class B : public QGLWidget
{
Q_OBJECT
public:
A *a;
C *c;
void paintGL();
B(QWidget *parent = 0);
}B::B(QWidget *parent) : QGLWidget(parent)
{
a = new A;
b = new B;
}void B::paintGL()
{
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glPushMatrix();
glLoadIdentity();
gluPerspective(70, width() / height(), 0.01, 1000);glMatrixMode(GL_MODELVIEW); glPushMatrix(); glLoadIdentity(); c->draw(a->point_s); glPopMatrix(); glMatrixMode(GL_PROJECTION); glPopMatrix();}
@
In class C I am defining the following. Maybe it doesnt make sense here but in my program it does and it is necessary.
@
class C
{
public:
C();void draw_points(QVector<Point3d> point); void draw(QVector<Point3d> point) const;};
C::C()
{
}void C::draw_points(QVector<Point3d> point)
{
int count =1;
double angle= 360/count;for(int i=0;i<5;i++) { glRotated(angle,0,1,0); draw(point); }}
void C::draw(QVector<Point3d> point) const
{
for(int i=0; i<point.size(); i++)
{
glBegin(GL_POINTS);
glVertex3f(point.value(i).x,point.value(i).y,point.value(i).z);
glEnd();
}
}
@
I hope you could help me now. Sorry for the late answer but I hadnt time the other days. The question still remains, why the array values get deleted.Thanks in Advance
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[quote author="basil_fawlty" date="1328362457"]Unfortunately all the elements are deleted as soon as I am leaving the constructor from class A.[/quote]
Most probably because you've declared the array on the stack, which means it is destructed once it gets out of scope.[quote author="basil_fawlty" date="1328362457"]I am defining an array with all its elements in the constructor of one class A. Now I want to use these values in my other class B.[/quote]
Two possibilities:- declare the array as member of the class
- create the array on the heap in the constructor, delete it in the destructor
In both cases you should use a getter instead of a public variable to comply with the rule of encapsulation.
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Sorry for my late update of the question,but I hadnt got time the other days. I thank you Lukas. I thought that my array is a member of my class.
So you are suggesting to use getters. I have never come across using getters in c++. It looks rather complicated. Maybe you could tell me a bit more how to create a getter.Thanks in advance
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Hm... Ok i have tried it like this:
In a.cpp:
@
QVector<Point3d> A::get_m()
{
return this->point_s;
}
@In a.h:
@
QVector<Point3d> get_m();
@In b.cpp:
@
b_points = a->get_m();
c->draw(b_points);
@Still the same. I am not getting it.
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[quote author="basil_fawlty" date="1328568251"]So you are suggesting to use getters. I have never come across using getters in c++. It looks rather complicated. Maybe you could tell me a bit more how to create a getter.[/quote]
It is nothing special. Just make your members private instead of public and add methods to get and set the value - like you did in your previous post.
Your code works fine (apart from some slips of the pen in A #1 and B #17). glVertex3f() is called with the values specified in A::A(). So your error is either in the way you set up your OpenGL viewport or in code not shown here.