Force a std::vector to free its memory?

Question

Possible Duplicates:
reduce the capacity of an stl vector
Is this normal behavior for a std::vector?

I know that std::vectors do not 'free' the memory when you call vector.clear(), but how can I do this? I want it to release all of its resources once I clear it but I don't want to destroy it.

Here is what is happening right now. I have a class called OGLSHAPE and I push these into a vector of them. I was hoping that once I did shapevec.clear() I'd get all my memory back, but only got 3/4 of it back. I'm not 100% sure if this is a memory leak or not so I want to free all the resources to be sure its not a leak. Thanks

score 16 · Accepted Answer · 2010-07-03T19:28:06.547

16

Use the swap trick:

#include <vector>

template <typename T>
void FreeAll( T & t ) {
    T tmp;
    t.swap( tmp );
}

int main() {
    std::vector <int> v;
    v.push_back( 1 );
    FreeAll( v );
}

edited Jul 03 '10 at 19:28

answered Jul 03 '10 at 19:19

1

Neil, is there a reason you're having `tmp` or is that just a question of style and personal preferences? – sbi Jul 03 '10 at 20:56
@sbi Both :-) And I think it's clearer. – Jul 03 '10 at 20:59
3

@Neil: Yeah, my wording was bad, I meant to ask whether there's a _technical_ reason. Anyway, thanks for answering. I might have been poisoned by the _C Terseness Virus_, but I actually do prefer `std::vector().swap(v)`. – sbi Jul 03 '10 at 21:08

score 2 · Answer 2 · edited Mar 03 '20 at 08:38

2

Consider using the swap trick:

std::vector<Shape>().swap(shapes);

edited Mar 03 '20 at 08:38

AndreyS Scherbakov

2,674
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answered Jul 03 '10 at 19:22

nas

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Force a std::vector to free its memory?

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