Object on stack unexpectedly gets deleted

Question

I'm getting a weird bug. My deconstructor is getting called whenever I create an object on the stack, and then use its "insert" function. The insert function does not delete anything. If I create the object on the heap and then call insert, the deconstructor is never called (which is what I want, obviously). This problem only occurs with my insert function. Other functions like empty () or size () do not provoke the same error.

I'm using Visual Studio 2012.

Where the problem occurs:

Map n;
n.insert(5, "5");
//Map deconstructor gets called unexpectedly

Where the problem does not occur

Map *n = new Map ();
n->insert (5, "5");
//Map deconstructor does not get called

code:

struct node
{
   int key;
   string value;
   node *left, *right;
};

//Note: I took away unrelated code from this function, b/c I narrowed down the problem 
void Map::insert (int key, string value)
{
  root = new node(); /**<-- This is the offending piece of code I think. If I comment it out, then the map deconstructor won't get called after the function exits*/
  root->key = key;
  root->value = value;
  root->left = NULL;
  root->right = NULL;
}
Map::~Map(void)
{
    cout << "Deconstructor being called";
}

Map::Map(void)
{
    root = NULL;
}

Is `n` going out of scope? You should put together a short complete example of what you're doing. — Retired Ninja, Oct 06 '14 at 05:04
you need to learn the language first. and for this question, learn the memory management part — Bryan Chen, Oct 06 '14 at 05:04
Can you provide [an example we can actually run](http://stackoverflow.com/help/mcve)? What you've posted is missing context we need to see to answer the question. — user2357112, Oct 06 '14 at 05:04
What happens if you *don't* call `insert`? How have you determined that `insert` has anything to do with your problem? — user2357112, Oct 06 '14 at 05:06
The comment for `root = new node();` in the general **`insert`** method should read: "Just leaked my prior root unless this is a new map". — WhozCraig, Oct 06 '14 at 05:19
possible duplicate of [Creating an object: with or without \`new\`](http://stackoverflow.com/questions/6337294/creating-an-object-with-or-without-new) — Félix Adriyel Gagnon-Grenier, Oct 06 '14 at 05:29

score 1 · Answer 1 · answered Oct 06 '14 at 05:27

1

This is how destructors work in C++

Automatic objects' destructors are called automatically. Dynamically allocated objects require you to delete them.

answered Oct 06 '14 at 05:27

codenheim

20,467
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score 0 · Answer 2 · answered Oct 06 '14 at 05:24

Whoops, I just realized that this actually is expected. After my main function (where the object is being instantiated and inserted into) exits, the deconstructor gets called automatically. This does not happen when object is created on the heap, unless I explicitly call delete. It happened only during insert because of a function that checks if the root is not NULL before going through with deconstructing the object. If there is no insert, the root is NULL, and function just exits.

Thanks a lot.

Object on stack unexpectedly gets deleted

2 Answers2