Deallocating heap memory from a vector.

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I have a vector in which I stored objects of structures. Now I need to deallocate the memory .
Kindly tell me how?

Posted 22-Oct-12 23:22pm

newbie@work

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2 solutions

Solution 1

Use the erase()[^] method on the items you wish to delete.

Posted 22-Oct-12 23:30pm

Richard MacCutchan

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Legor 23-Oct-12 6:23am

I allways thought one has to use the erase-remove idiom to really delete something from a vector and not just decreasing the capacity. Is erase() alone really enough?
http://en.wikipedia.org/wiki/Erase-remove_idiom

Richard MacCutchan 23-Oct-12 6:30am

Quite possible, I have not checked it thoroughly, something to check later. I provided the link to MSDN so OP could do so.

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CPallini · Accepted Answer · 2012-10-22T23:38:00

Solution 2

Memory will be released by vector destructor (unless you have stored pointers inside the vector).
If your vector contains just pointers to the objects (since your are telling us the objects are heap allocated) then you have to delete every pointer (make a loop on vector items).

Posted 22-Oct-12 23:38pm

CPallini

Updated 22-Oct-12 23:41pm

v2

Comments

newbie@work 23-Oct-12 5:43am

I am trying to iterate. I am doing something wrong I guess. Please see this
for(it=Vector.begin();it!=Vector.end();it++)
{

delete *it;
Vector.erase(it);

}

CPallini 23-Oct-12 6:02am

never call vector.erase this way: "Because vectors keep an array format, erasing on positions other than the vector end also moves all the elements after the segment erased to their new positions, which may not be a method as efficient as erasing in other kinds of sequence containers (deque, list).

This invalidates all iterator and references to position (or first) and its subsequent elements." ( http://www.cplusplus.com/reference/stl/vector/erase/ ).

You should instead write:
for (it=Vector.begin(); it != Vector.end(); it++)
delete *it;
Vector.erase(it.begin(), it.end());

Note that last step (Vector.erase()) is hardly needed, because Vector destructor will care about.

Legor 23-Oct-12 6:23am

I allways thought one has to use the erase-remove idiom to really delete something from a vector and not just decreasing the capacity. Is erase() alone really enough?
http://en.wikipedia.org/wiki/Erase-remove_idiom

CPallini 23-Oct-12 6:39am

Nope (at least as far as I know), as stated by the page you linked: "A common programming task is remove all elements that have a certain value or fulfill a certain criterion from a collection."
This is a very special case and you are using first remove for selecting (and moving) the elemens inside the collection and then erase to make sure the elements are really 'removed'. If you don't need (as in the OP case) to selectively remove the elements then you just use erase.

Legor 23-Oct-12 7:06am

Yes i think you're right about that.

CPallini 23-Oct-12 7:57am

About that? I'm always right!

:-D

Legor 23-Oct-12 8:55am

As far as i can say from CP I think you're right in many things (in the fields of programming) ;)

newbie@work 23-Oct-12 6:27am

All right! Thanks

CPallini 23-Oct-12 6:41am

You are welcome.

JackDingler 23-Oct-12 15:57pm

You can call Vector.clear() to erase all of the elements.
Vector.reserve(size_t) will attempt to change the allocated size of the vector, without changing the number of elements, unless the number of elements is greater than the new size.