Re: Is there a memory leak in this code ?

Diwa <>
Fri, 28 Dec 2007 12:40:39 -0800 (PST)
On Dec 28, 3:23 pm, Erik Wikstr=F6m <> wrote:

On 2007-12-28 20:32, Diwa wrote:

On Dec 28, 2:15 pm, "Victor Bazarov" <> wrote:

Diwa wrote:

// -----------------------------------

class Column
   string name;
   vector<int> values;

// -----------------------------------

void loadValues()

    Column *p = new Column();

 p->values.push_back(55); // <--- Line 1
 p->values.push_back(66); // <--- Line 2

 delete p; // <--- Line 3

// -----------------------------------

Are the values inserted (Line 1 and 2) on
 the stack or on the heap ?

Values that the container
'p->values' stores are _always_ in the free store, the vector
allocates all its values there, unless you provide some kind
of custom allocator, which you didn't.

Is there a memory leak for the two inserted
 values inspite of the "delete p" at line 3 ?


I suspect there is a memory leak. Here is my reasoning.

When "Column *p = new Column( )" is done it allocates,
  lets say, 20 bytes. Just before the memory address
  returned by "new", maybe it stores the num of bytes.

The "push_back()" done later at line 1 and line 2 may
  results in some more "new" but still it will not
  change the value (num of bytes) just before addr "p"

So at line 3, when "delete p" executes, it sees the
  velue "20" just before p and then deletes only 20

Am I missing something ?

Yes, when you push back the numbers on line 1 and 2 those are stored in
memory managed by the vector 'values'. When you, on line 3, delete p it
will call the destructor of the Column class pointed to by p. When this
happens it will call the destructors of its members 'name' and 'value'.
When the vector's destructor is run it will free whatever memory was
used by the vector, including that used to store the elements that you
pushed back on line 1 and 2. You only have to worry about the memory you
explicitly allocated using new, nothing else.

Ah, now I feel stupid. Obviously, when 'delete p' is done it
  will invoke the dtor of "Column" class in which case all
  memory deletion is taken care of automatically. I don't why
  but my brain was processing the behaviour of "delete p" as
  behaviour of "free p". Thanks anyways, Erik and Victor.

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