How to delete objects from vector of pointers to object? [duplicate]

Question

I am trying to understand how to delete a vector of pointers, and the pointed objects, in memory. I have started with a simple example, found in another thread, but I get "pointer being freed was not allocated" error.

What I am doing wrong?

#include <vector>
#include <algorithm>
#include <iostream>

int main(){
    std::vector <int *> vec;

    int a = 2;
    int * b = &a;

    int c = 3;
    int * d  = &c;

    vec.push_back(b);
    vec.push_back(d);

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

}

You only delete if you new'd.

user529758
– user529758

2013-07-07 22:41:01 +00:00
Commented Jul 7, 2013 at 22:41 — user529758
– user529758, Commented Jul 7, 2013 at 22:41

Community · Accepted Answer · 2017-05-23 11:56:32Z

3

Only call delete on variables that were created with new Check this link: Calling delete on variable allocated on the stack

edited May 23, 2017 at 11:56

CommunityBot

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answered Jul 7, 2013 at 22:33

hanslovsky

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3 Comments

Béatrice M. Over a year ago

OK - So if instead of a vector of int *, I had some Objects * (instantiated by new), then it would have worked?

Yakk - Adam Nevraumont Over a year ago

@Bibi541 If you had a vector of int* full of elements instantiated by new, it would have worked. int* just means "address of an int" -- not "reference to an int I own".

Qaz Over a year ago

@Bibi541, Then you'd realize that cleaning them up yourself was a royal pain, especially in terms of exception-safety, and you'd use a smart pointer and live happily forever after.

user123 · Accepted Answer · 2013-07-07 22:33:42Z

2

You're deallocating memory that was allocated on the stack with automatic storage. That's why you're getting errors.

Only delete things you allocated with new. RAII will take care of the rest.

answered Jul 7, 2013 at 22:33

user123

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Comments

Zijun · Accepted Answer · 2013-07-07 22:43:42Z

0

When you do

int a = 2;

You are allocating a int on stack and anything on stack does not need to delete, it will be freed automatically once we left the scope it is declared. Therefore in your code, you are trying to free the same thing twice.

Whilst if you do

int* a = new int(2);

You will then allocate a int on heap, where data will not be deleted unless you explicitly call delete.

The bottom line is, new and delete should always be written in pairs.

answered Jul 7, 2013 at 22:43

Zijun

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