How can I enqueue and dequeue a class with QPoint pointer members?

manpreet Best Answer 2 years ago

I would like to use a QQueue to store objects of my class. The class has members that are pointers to QPoints. I store an object of my class in a QQueue and retrieve it.

#include <QQueue>
#include <QPoint>
#include <QDebug>

class Foo {
public:
    Foo(int x, int y);
    ~Foo();
    QPoint bar;
    QPoint* baz;
    //Q_DISABLE_COPY(Foo)  // not sure whether I need this
};

Foo::Foo(int x, int y): bar(x, y) {
    baz = new QPoint(x, y);
}

Foo::~Foo() {
    delete this->baz;
}


int main(void) {
    QQueue<Foo> queue;
    Foo a(5, 6);
    qDebug() << "a.bar.x()=" << a.bar.x() << ", a.baz->x()=" << a.baz->x();

    queue.enqueue(a);
    Foo b = queue.dequeue();
    qDebug() << "b.bar.x()=" << b.bar.x() << ", b.baz->x()=" << b.baz->x();

    return 0;
}

Output:

a.bar.x()= 5 , a.baz->x()= 5
b.bar.x()= 5 , b.baz->x()= 0
09:46:59: The program has unexpectedly finished.

If I comment out delete this->baz; in the destructor I get what I would have expected:

a.bar.x()= 5 , a.baz->x()= 5
b.bar.x()= 5 , b.baz->x()= 5

Could someone explain what's going on here? It seems to me that the destructor to Foo is being called early. Thanks.

manpreet 2 years ago

QQueue stores a copy of the added object. So, at this line Foo b = queue.dequeue(); destructor of Foo is called. You can ensure in this in debugger. Add breakpoint to Foo destructor and debug.