Vector of std::shared_ptr not freeing memory

Question

First time posting on here, and I'm not a CS guy, so please bear with me. I have a good sized, code, so I will post a bare-bones version of my problem below and then explain it.

#include <vector>
#include <memory>

class A{

public: 
  A(){};
  double dbl[20];
};

typedef std::shared_ptr<A> A_ptr;

class B{
  public:
  const std::vector<A_ptr> createAVector(){
    std::vector<A_ptr> vec;
    for(int i=0; i<4; i++){
      vec.push_back(A_ptr( new A() ));
    }
    return vec;
  }
};

int myfunc(){

  // Do Stuff...

  std::vector<A_ptr> globvec;

  B b;
  for(int i=0; i<1e6; i++){
    const std::vector<A_ptr> locvec = b.createAVector();

    for(int i=0; i<locvec.size(); i++) globvec.push_back(locvec[i]);

  }

  globvec.clear();
  globvec.shrink_to_fit();

  // Do more stuff...

  return 1;
}


int main(){

  myfunc();

  for(auto i=0; i<3; i++){
    myfunc();
  }
  return 1;
}

Edit: I modified the code so it actually compiles.

So, basically I have two classes. Class A stores the actual data. Class B, among other things, creats a vector of std::shared_ptrs to A and returns it. I then assemble these local vectors into a large global vector in a function called myfunc. To test that memory is freed when I want to shrink the size of globA, I call globA.clear() and globA.shrink_to_fit().

The problem is that calling clear() and shrink_to_fit() does not free the memory of all the A's created.

Am I doing something obviously wrong here? Any idea what might be going on?

Any help would be greatly appreciated.

Thanks!

John

Answer 1

Your code is fine. You can essentially 'prove' that you are not leaking A objects with this... (I also had to reduce the number of iterations from 1e6 to get any reasonable runtime).

There are more sophisticated tools for finding memory leaks. I know for Linux we use Valgrind. I don't know what the Windows equivalent is however.

class A{

public: 
  A() { std::cout << "Created A " << ++num_instances << std::endl;}
  ~A() { std::cout << "Destroyed A " << --num_instances << std::endl;}

  static int num_instances; // So not thread-safe

  double dbl[20];
};

int A::num_instances = 0;