clearing a vector of pointers [duplicate]

Question

This question already has answers here:

How to avoid memory leaks when using a vector of pointers to dynamically allocated objects in C++? (4 answers)

Closed 3 years ago.

Assume I have defined a class like this:

 class foo {
 private: 
    std::vector< int* > v;
 public:
    ...
    void bar1()
    {
       for (int i = 0; i < 10; i++) {
         int *a = new int;
         v.push_back( a );
       }
    };

    void bar2()
    {
       std::vector< int >::iterator it = v.begin();
       for ( ; it != v.end(); it++ )  
         std::cout << (*it);
       v.clear();
    }
 };

In short, I push back some pointers in a vector, later I clear the vector. The question is, does this code has memory leak? I mean by clearing the vector, are the pointers deleted properly?

Answer 1

I think the shortest and clearest solution would be:

std::vector<Object*> container = ... ;
for (Object* obj : container)
    delete obj;
container.clear();

Answer 2

Yes, the code has a memory leak unless you delete the pointers. If the foo class owns the pointers, it is its responsibility to delete them. You should do this before clearing the vector, otherwise you lose the handle to the memory you need to de-allocate.

   for (auto p : v)
   {
     delete p;
   } 
   v.clear();

You could avoid the memory management issue altogether by using a std::vector of a suitable smart pointer.

Answer 3

You can use for_each :

std::vector<int*> v;

template<typename T>
struct deleter : std::unary_function<const T*, void>
{
  void operator() (const T *ptr) const
  {
    delete ptr;
  }
};

// call deleter for each element , freeing them
std::for_each (v.begin (), v.end (), deleter<int> ());
v.clear ();

Answer 4

Nope you only clear the vector storage. Allocated memory with 'new' is still there.

for (int i =0; i< v.size();i++)
   {
     delete (v[i]);
   } 
   v.clear();