Delete all items from a c++ std::vector


Question

I'm trying to delete everything from a std::vector by using the following code

vector.erase( vector.begin(), vector.end() );

but it doesn't work.


Update: Doesn't clear destruct the elements held by the vector? I don't want that, as I'm still using the objects, I just want to empty the container

1
59
6/7/2016 7:15:40 AM

Accepted Answer

I think you should use std::vector::clear:

vec.clear();

EDIT:

Doesn't clear destruct the elements held by the vector?

Yes it does. It calls the destructor of every element in the vector before returning the memory. That depends on what "elements" you are storing in the vector. In the following example, I am storing the objects them selves inside the vector:

class myclass
{
public:
    ~myclass()
    {

    }
...
};

std::vector<myclass> myvector;
...
myvector.clear(); // calling clear will do the following:
// 1) invoke the deconstrutor for every myclass
// 2) size == 0 (the vector contained the actual objects).

If you want to share objects between different containers for example, you could store pointers to them. In this case, when clear is called, only pointers memory is released, the actual objects are not touched:

std::vector<myclass*> myvector;
...
myvector.clear(); // calling clear will do:
// 1) ---------------
// 2) size == 0 (the vector contained "pointers" not the actual objects).

For the question in the comment, I think getVector() is defined like this:

std::vector<myclass> getVector();

Maybe you want to return a reference:

// vector.getVector().clear() clears m_vector in this case
std::vector<myclass>& getVector(); 
100
8/28/2013 8:27:10 AM

vector.clear() should work for you. In case you want to shrink the capacity of the vector along with clear then

std::vector<T>(v).swap(v);

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