Exception when adding QGraphicsItem to stage?

Question

Qt

ball class:

#endif // BALL_H

ball.cpp:
#include "ball.h"

ball::ball(int x, int y,int R)
{
    this->x=x+10;
    this->y=y;
    this->R=R;
    ballObj = new QGraphicsEllipseItem(x,y,R,R);

}
void ball::setPos(int newX, int newY)
{
    this->x=newX;
    this->y=newY;
}
void ball::setSpeed(int newSpeed)
{
    this->speed=newSpeed;
}
QGraphicsEllipseItem* ball::getBall()
{
    return  this->ballObj;
}
QPoint ball::getPos()
{
    return QPoint(this->x,this->y);
}
int ball::getSpeed()
{
    return  this->speed;
}

Object creation:

ballObj=new ball(0,this->height(),10);

    gameBoard->scene()->addItem( ballObj->getBall());

The constructor - works fine - looked under the debugger: a

screenshot of the next step after the breakpoint is triggered
, but when I try to add it to the scene, I get a SegmentationFault - see the screenshot:

Answer 1

In C++, all pointers must be checked for null before use. You obviously have some kind of null pointer.
This code still looks suspicious:

allObj=new ball(0,this->height(),10);
gameBoard->scene()->addItem( ballObj->getBall());

The result of new is assigned to one variable, and then another is used. I assume this is a typo.
As I already wrote above, you need to check the result of the scene() call for null (most likely, this is where the error is), as well as the gameBoard itself.
And one more thing, you should understand that after calling the addItem(ballObj->getBall()) method, the returned object will go under the control of the scene (this is written in the documentation) and can be deleted at any time. That being said, who should remove ballObj in your code is not clear.
PS
This is no exception.