Memory release of boost::shared_ptr of std::vector

Question

I'm trying to release the memory of a boost::shared_ptr<std::vector<std::vector<std::vector<int> > > > using the following code:

vec->clear();
std::vector<std::vector<std::vector<int> > > (*vec).swap(*vec);

But for some reason it isn't working. I checked with htop command and the memory used is the same as I've never released the object.

Then I tried to release each vector separately like:

for (auto it1 : *vec) 
{
    for (auto it2 : it1)
    {
        it2.clear();
        std::vector<int>(it2).swap(it2);
    }
    it1.clear();
    std::vector<int>(it1).swap(it1);
}   

But still consumes the same amount of memory.

Am I doing something wrong? Maybe it has to do with the shared_ptr because I've released vectors without pointers before and it worked.

Update

The shared_ptr won't get out of scope since is a class member of an object that remains in execution in a sleeping thread.

Answer 1

If you have a std::shared_ptr<std::vector>> and you want to delete it:

std::shared_ptr<std::vector<T>> ptr = ...;
ptr.reset();

If you have a std::vector<std::shared_ptr<T>> and you want to empty it:

std::vector<std::shared_ptr<T>> vec = ...;
vec.clear();

If you have a std::vector<T> and you want the vec.capacity() == vec.size() :

std::vector<T> vec = ...;
vec.shrink_to_fit(); // or: std::vector<T>(vec).swap(vec);

If you are concerned that htop doesn't show a reduced amount of allocated memory to the process, then let's just mark this as a duplicate of this post: vector<string> does not clear memory after out of scope