Memory free

Christian Ehrlicher

I cleared list when I delete MyClass, but they took the memory and did not release.

Which is basic c++. Why do you create the container on the heap at all? That's unusual, not needed and error prone as you can see.

Joe von Habsburg

@Christian-Ehrlicher said in Memory free:

Which is basic c++. Why do you create the container on the heap at all? That's unusual, not needed and error prone as you can see.

I have 2 thing. Firstly a class => MyClass
Secondly => ClassController (another QObject)

My system like that:

//MyClass
class MyClass : QObject{
 MyClass(){
someThingPointer = new SomeThingPointer ;
   someThingList = new SomeThingList<double>;
 };
~MyClass(){
someThingPointer->deleteLater();
    delete someThingList ;
 };

void doSth();

private :
 SomeThingPointer *someThingPointer;
 SomeThingList<double> *someThingList;
}

//ClassController
class ClassController: QObject{
 ClassController();
~ClassController();

void run();

public slots:
void addNew();
void deleteLast();

private :
QList<MyClass *> myClasses;
}


//MainWindow
void on_add_click(){
 emit addNew();
}

void on_delete_click(){
 emit deleteLast();
}

Where should I create new list? I create in constructer

@Christian-Ehrlicher said in Memory free:

Why do you create the container on the heap at all?

What do you mean by that? Can you explain?

jsulm

@Joe-von-Habsburg said in Memory free:

What do you mean by that? Can you explain?

Basic C++ stuff:

// This creates a member variable which is a pointer to a list
// If you then do someThingList = new ... you allocate memory on the heap
SomeThingList<double> *someThingList;

And the question was: why do you allocate someThingList on the heap? So, why is someThingList a pointer and not simply:

SomeThingList<double> someThingList;

Don't use pointers if they are not really needed...

Joe von Habsburg

@jsulm said in Memory free:

Don't use pointers if they are not really needed...

Because I couldn't change the indexes. When I first created this class for the first time, it was simple (no pointers). But then I realized that I can't change the indexes.

void run(){
  for(int i = 0; i < myClasses.size(); i++){
    MyClass *mc = myClasses.at(i);
    mc->someThingList()[25] = 10000;
  }
}

Do you have an advice?

jsulm

@Joe-von-Habsburg said in Memory free:

Because I couldn't change the indexes.

What does this have to do with pointers?
This should work just fine (don't know why you put () there):

mc->someThingList[25] = 10000;

But as far as I can see you did not explain what SomeThingList is exactly.

Joe von Habsburg

@jsulm said in Memory free:

don't know why you put () there

because it is private and access with getter.

@jsulm said in Memory free:

What does this have to do with pointers?

It could not work, but I will try again for you :)

Thanks for eveything

@jsulm said in Memory free:

What does this have to do with pointers?

I tested. for example :

for(int i = 0; i < myClasses.size(); i++){
  MyClass *mc = myClasses.at(i);
  for(int j = 0; j < size; j++){
    mc ->myList().append(x);
  }
  qDebug() << mc ->myList().size(); // 0
}

I can't add new data to mc ->myList() in classcontroller

jsulm

@Joe-von-Habsburg said in Memory free:

qDebug() << mc ->myList().size(); // 0

If you mean size() returns 0 then this simply means that size variable has 0 as value, so the inner for loop is never executed. Another explanation would be that myList() returns a COPY of the container, so you add to the copy (it should either return pointer to the container or reference). Again, has nothing to do with pointers...

Joe von Habsburg

@jsulm said in Memory free:

so the inner for loop is never executed. Another explanation would be that myList() returns a COPY of the container, so you add to the copy (it should either return pointer to the container or reference). Again, has nothing to do with pointers...

how can I append new data to my list ? when I use pointer list, its work, but if do not use pointer, I can not append new data

@SimonSchroeder said in Memory free:

it will create a copy that is returned and you'll only change the copy. With a reference you'll change the underlying list:

thank you

SimonSchroeder

@Joe-von-Habsburg said in Memory free:

I can't add new data to mc ->myList() in classcontroller

You need to make sure that MyClass::myList() returns a reference to the list. If you have something like:

class MyClass
{
  //...
  SomeThingList<double> myList() { return someThingList; }
}

it will create a copy that is returned and you'll only change the copy. With a reference you'll change the underlying list:

class MyClass
{
  //...
  SomeThingList<double>& myList() { return someThingList; }
}

jsulm

@Joe-von-Habsburg You should really learn C++.
See what @SimonSchroeder wrote...