clean correctly a QVector

Question

I have a QVector

QVector<const ClassA*> list;

and I want to know how it is what the best way to clean an QVector in this case.

ClassA is not a QObject.

Are you creating those pointers with `new`? If so, I suggest you look into either `std::unique_ptr`, `std::shared_ptr`, or their Qt counterparts. — NathanOliver, Jul 07 '20 at 12:25
The best way is to use Qt algorithm `qDeleteAll()` defined in . It only applies `delete` on all of the vector's elements. You need to call `QVector::clear()` if that's necessary. If the vector-object is going to be destroyed, only `qDeleteAll()` is sufficient — Pie_Jesu, Jul 07 '20 at 14:58

score 2 · Answer 1 · edited Jul 07 '20 at 13:26

2

Have a look at the documentation of QVector.clear() - I think it answers your question quite well.

To preserve it, I copied it here:

void QVector::clear()

Removes all the elements from the vector.

Note: Until Qt 5.6, this also released the memory used by the vector. From Qt 5.7, the capacity is preserved. To shed all capacity, swap with a default-constructed vector:

QVector<T> v ...;
QVector<T>().swap(v);
Q_ASSERT(v.capacity() == 0);

or call squeeze().

edited Jul 07 '20 at 13:26

Waqar

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answered Jul 07 '20 at 12:25

KYL3R

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in this case clear() release only the pointer list from the vector but it not free the memory since the pointer is manually reserved. I try to do something like that for (int index = 0; index < mList.count(); ++index ) { const ClassA* value = const_cast(mList[index ]); delete value ; } – adir Jul 07 '20 at 12:53

score 2 · Accepted Answer · answered Jul 07 '20 at 14:50

2

Here it is in two lines of code:

while (list.count())
     delete list.takeLast();

answered Jul 07 '20 at 14:50

smacker

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score 1 · Answer 3 · answered Jul 08 '20 at 08:51

I would write :

qDeleteAll(list);
list.clear();

I also advise you to read this post (as you may get something interesting from it) : Does C++11 allow vector<const T>?

EDIT (a few secondes after post) : My apologies to Pie_Jesu who posted a (very) similar comment on the question, which I did not read when I was writting this answer.

adir · Answer 4 · 2020-07-07T13:27:13.190

0

in this case clear() release only the pointer list from the vector but it not free the memory.

I try to do something like that

for (int index = 0; index < mList.count(); ++index )
{
    const ClassA* value = const_cast<ClassA*>(mList[index ]);
    delete value ;
}

edited Jul 07 '20 at 13:27

answered Jul 07 '20 at 12:51

adir

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score 0 · Answer 5 · edited Jul 07 '20 at 13:26

0

I would simply suggest loop with a for each over it and delete every pointer. after that clear the vector

for(auto item : list){
    delete item;
}
list.clear();

Or simply use QScopedPointer elements of classA in your list and simply call clear().

edited Jul 07 '20 at 13:26

Waqar

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answered Jul 07 '20 at 13:03

tscheppe

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that can work if the QVoctor contain a pointer of ClassA **QVector** but in my case the QVector contain a const of **ClassA**. – adir Jul 07 '20 at 14:05

clean correctly a QVector

5 Answers5