clearing a vector of pointers

Question

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?

You actually push only a single pointer to the vector; the `for` loop in `bar1` only executes the `new int;` line since it has no curly braces, and `i+++` is a syntax error and... ah well, I guess this is meant to be pseudocode. — Frerich Raabe, Oct 09 '12 at 07:53
You also need a vector of int pointers: `std::vector< int* > v;` instead of `std::vector< int > v;` — juanchopanza, Oct 09 '12 at 08:00

juanchopanza · Accepted Answer · 2019-05-15T19:14:25.087

74

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.

edited May 15 '19 at 19:14

answered Oct 09 '12 at 07:48

juanchopanza

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can you please give me straghit method (not the smart ptr)?? – mahmood Oct 09 '12 at 07:52
@mahmood It depends on the details of your class, but it is a safe bet that you should do it just before clearing the vector. Iterate over it, deleting each element. *Then* clear it. – juanchopanza Oct 09 '12 at 07:52
Should this be `std::vector< int* >::iterator`? – scohe001 May 15 '19 at 18:56
@scohe001 Yes indeed, thanks! I transformed it into C++11 to bypass the issue entirely. – juanchopanza May 15 '19 at 19:14
When to do that vs having to write p = nullptr for example ? – Hussein Hammoud Dec 17 '22 at 20:22

score 15 · Answer 2 · answered Oct 01 '15 at 16:06

15

I think the shortest and clearest solution would be:

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

answered Oct 01 '15 at 16:06

Tim Kuipers

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score 10 · Answer 3 · 2012-10-09T08:01:10.073

10

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();

edited Oct 09 '12 at 08:01

answered Oct 09 '12 at 07:48

1

use 'delete' on each iteration. After than use clear to clear the vector. e,g delete(*it) – Oct 09 '12 at 07:52
for (auto& i : v) { delete (i); } v.clear(); is this code correct – lsrawat Aug 05 '17 at 06:41

score 6 · Answer 4 · answered Oct 09 '12 at 07:52

6

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 ();

answered Oct 09 '12 at 07:52

tozka

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I often wish something like this `deleter` was readily available; I wonder, could you implement it in terms of `std::mem_fun_ptr or `std:fun_ptr` or so? – Frerich Raabe Oct 09 '12 at 07:55

clearing a vector of pointers

4 Answers4

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