Re: Deleting elements of vectors that contain pointers to other
objects
On Mar 19, 5:46 pm, red floyd <redfl...@gmail.com> wrote:
On Mar 19, 9:39 am, dwightarmyofchampi...@hotmail.com wrote:
How exactly do I delete elements of a vector in the
destructor? Suppose my vector in my class definition looks
like this:
std::vector<ABC*> vec;
which means I am declaring a vector whose elements will
contain pointer to ABC objects.
...and in my constructor I have:
vec.clear(); // make sure vector is empty before populating it
for (int i = 0; i < 5; i++)
{
ABC* abcobject1 = new ABC(i);
vec.push_back(abcobject1);
}
When I go to my destructor, do I just need to pop_back() the
vector elements...
for (int i = 0; i < 5; i++)
{
vec.pop_back();
}
...or do I delete each ABC object and then pop_back its
corresponding vector pointer...
for (int i = 0; i < 5; i++)
{
delete vec[i]; vec[i] = 0; // or is it (*vec[i])???
vec.pop_back();
}
...or do I do something else? Isn't there a delete[]
statement for this sort of thing?
This is a question of ownership. That's why you need to
document who owns what. If the vector is intended to own the
pointers, you probably shouldn't store raw pointer, but
instead use your favorite smart pointer.
Sort of. If the objects in question have value semantics, and
support copy, then he probably shouldn't have a vector of
pointers to begin with. If they are entity objects, then you
have to ask the question of what their lifetime should be. In
practice, cases where the lifetime of an entity object depends
on the lifetime of a container are extremely rare.
If the lifetime does depend strictly on the container of course,
then you need to wrap the container in a class which takes care
of the deletes.
If you're using raw pointers, you need to delete the elements
individually.
for (std::vector<ABC*>::iterator it = vec.begin();
it != vec.end();
++it)
{
delete *it;
*it = 0; // probably optional
}
Actually, formally speaking, even that's undefined behavior.
Formally, you can't touch the vector once you've done the
delete; you have to erase the element, or replace it with a null
pointer, first.
Practically, if this code is in the destructor of the object
containing the vector, I wouldn't worry about it.
If you're using smart pointers, where smart_ptr_t<> is your
favorite smart pointer:
std::vector<smart_ptr_t<ABC> > vec;
Then, when vec is deleted, it invokes the smart_ptr_t<>
destructor on every element, and the smart_ptr_t<> destructor
handles the memory management.
Supposing it's that type of smart pointer:-). (Don't forget
that smart pointers are used for other things, such as managing
locks.) This is a workable solution, but it's usually overkill,
and you have to pay attention to the semantics of the
smart_ptr---those which would seem to have the appropriate
semantics (e.g. auto_ptr) often don't work in containers.
--
James Kanze (GABI Software) email:james.kanze@gmail.com
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