issue regarding deleting an object in qt with delete and free

[sierdzio]

@SherifOmran said in issue regarding deleting an object in qt with delete and free:

ClassList::ClassList()
{

//main
head = new Node;
head=NULL;

Huh? Looks like an instant memory leak.

(btw. you should use nullptr)

Frankly, I don't have time to analyse your whole code, sorry. But perhaps try running it through valgrind and address sanitizer - it should pick all the leaks for you.

[jsulm]

@SherifOmran As far as I can see you did not initialise temp and try to delete it! No wonder it does not work.

ClassList::ClassList()
{
    head = new Node;
    head=NULL; // Why do you assign NULL after creating instance?!
}

ClassList::~ClassList()
{
    delete temp; //Check whether temp points to anything before deleting
    delete head;
}

Change

private:
    Node* head = nullptr; //number 1
    Node* current = nullptr; //current node
    Node* temp = nullptr;
    Node* temp2 = nullptr;

[SherifOmran]

what caused confusion is that i delete L at line 51 and it was accepted

[SherifOmran]

@jsulm
because i want to check that the head it Null at the initialization

[jsulm]

@SherifOmran

delete L; // L became a null pointer

The comment is wrong: the value of the pointer does not change when you call delete on it.

delete L;
L = nullptr; // Now it is null pointer

[SherifOmran]

yes thank you i corrected this comment

[jsulm]

@SherifOmran said in issue regarding deleting an object in qt with delete and free:

@jsulm
because i want to check that the head it Null at the initialization

As @sierdzio already told you: you created a memory leak this way.
Just remove

head = new Node;

Else you create an instance and loose the pointer to it, so you never delete this instance -> memory leak.

[SherifOmran]

yes i see.
how i delete temp that was initialized in ClassList::InsertNode ?

[jsulm]

@SherifOmran said in issue regarding deleting an object in qt with delete and free:

how i delete temp that was initialized in ClassList::InsertNode ?

delete temp;

[JonB]

@SherifOmran

how i delete temp that was initialized in ClassList::InsertNode ?

As @jsulm says it's still delete temp, but make sure you initialize temp = nullptr in either the declaration or the constructor, ClassList::InsertNode might never get called....

[SherifOmran]

thank you guys for suggested corrections