Removing custom widget from QList, will it be deleted from memory?

Jc_Opc

Hi,
This is a quick question, I am still working on my C++ and QT skills, this is the thing, I created a list of custom widgets,
QList<cWidget*> list; then I created a function to add the widgets:

parent::addwidget(int id){
    cWidget *p_widget = new cWidget(id, this); 
    list.append(p_widget);
}

If I use list.removeAt(id) will delete the *p_widget from memory too?

Thanks

JonB

@Jc_Opc

@SGaist said in Removing custom widget from QList, will it be deleted from memory?:

It's not the job of QList to manage the memory of an object behind a pointer, that is yours.

This is the important thing. The fact you put the object into/take it out of a QList<> simply has no effect on the situation if there were no list.

You went:

cWidget *p_widget = new cWidget(id, this);

so in principle it's your responsibility to delete it. In this case, if you have attached it to the parent by passing this, so alternatively it will get deleted if/when that gets deleted.

SGaist

Hi,

No, there's no reason for it to delete anything. You just remove the pointer from the list. It has nothing to do with the object being pointed at.

Jc_Opc

@SGaist thanks, the obvious question would be, what about the memory where those objects are being stored? should it be free?

SGaist

Do you mean the memory used to store the pointer internally in your a QList ?

Jc_Opc

No, the memory of object when it was created. I assuming that QList can handle its memory resources properly.

SGaist

It's not the job of QList to manage the memory of an object behind a pointer, that is yours.

SGaist

@Jc_Opc said in Removing custom widget from QList, will it be deleted from memory?:

No, the memory of object when it was created. I assuming that QList can handle its memory resources properly.

We might be talking of two different things please clarify what you have in mind with a code sample.

JonB

@Jc_Opc

@SGaist said in Removing custom widget from QList, will it be deleted from memory?:

It's not the job of QList to manage the memory of an object behind a pointer, that is yours.

This is the important thing. The fact you put the object into/take it out of a QList<> simply has no effect on the situation if there were no list.

You went:

cWidget *p_widget = new cWidget(id, this);

so in principle it's your responsibility to delete it. In this case, if you have attached it to the parent by passing this, so alternatively it will get deleted if/when that gets deleted.

Jc_Opc

thank you all, that was the reason why I put this, but bear with me a little more, I just want to know how to manage memory heap properly when using a containers (good practices). This is my attempt deleteWidget() function assuming that I am not using this when creating the widget so I would do:

After leaving the addWidget function, I only have the list of widgets, so here it is:

void parent::deleteWidget(int id){
       delete list.at(id);
       list.removeAt(id);
}

The reason of my confusion is because I always created each widget with its own pointer name, in here the name is the same but stored dynamically in a container.

SGaist

@Jc_Opc said in Removing custom widget from QList, will it be deleted from memory?:

void parent::deleteWidget(int id){
delete list.at(id);
list.removeAt(id);
}


void parent::deleteWidget(int id){
       QWidget *widget = list.takeAt(id);
       delete widget;
}

Would be cleaner. You can even make it a one liner.

One unrelated thing: please use meaningful name for classes and variables. It will make your code easier to work with.

Jc_Opc

@SGaist Thanks, in my code the names are different, and are kind of harder to understand based on the context, I am still learning how to name objects properly though; looking at others codes and practice will do the trick. In here I just wanted to learn the principles and your answer and @JonB's helped me a lot.

The time you guys take to answer all these questions are very appreciated.