How to deallocate the dynamically allocated classes?

Question

I have this simple program below:

#include <iostream>            
using namespace std;

class pithikos {

public:
    //constructor
    pithikos(int x, int y){
        xPosition = x;
        yPosition = y;
    }

    //multiplicator of x and y positions
    int xmuly(){
        return xPosition*yPosition;
    }   

private:
    int xPosition;
    int yPosition;
};

int main(void){


//alloccate memory for several number of pithikous
pithikos **pithik = new pithikos*[10];
for (int i = 0; i<10; i++){
     pithik[i] = new pithikos(i,7);
}

cout << pithik[3]->xmuly() << endl; /*simple print statement for one of the pithiks*/

//create pithikos1 
pithikos pithikos1(5,7);
cout << pithikos1.xmuly() << endl;

//delete alloccated memory
for (int i=0; i<10; i++) delete pithik[i];
delete [] pithik;
cout << pithik[4]->xmuly() << endl;
}

The class just takes two numbers and multiplies them and return the value. But I want the oblects to born and die.

So I allocated in this example 10 objects (pithikos) and then I am testing weather it works.

when I ran the program I get this:

21

35

28

my problem is: why do I get the value 28 after I used the command?

delete [] pithik;

how can I delete the objects if not like this?

`delete` does delete the object, and you are not allowed to dereference the pointer after that — 463035818_is_not_an_ai, Feb 14 '19 at 21:11
https://stackoverflow.com/questions/1930459/c-delete-it-deletes-my-objects-but-i-can-still-access-the-data — hegel5000, Feb 14 '19 at 21:13
btw your program is not simple at all. Using `std::vector` is simple, using a `pithikos **` is complicated, error prone and dangerous — 463035818_is_not_an_ai, Feb 14 '19 at 21:13
Here is a different link that describes a similar undefined behavior situation (where you are able to access memory that you believe you should not have access): https://stackoverflow.com/a/6445794/487892 — drescherjm, Feb 14 '19 at 21:16
It's always humorous to me when I see a new C++ programmer expects the memory to just disappear into thin air when using `delete`. — PaulMcKenzie, Feb 14 '19 at 21:24
Don't think the linked question answers this specific question. — Martin York, Feb 14 '19 at 21:24
@MartinYork the question doesnt answer the question, but the answer does :P. Dont like the accepted answer too much either, but I think the second one explains a bit. If not there must be a better dupe — 463035818_is_not_an_ai, Feb 14 '19 at 21:26
@PaulMcKenzie maybe `free` would have been a better name for what `delete` does, unfortunately that was already taken ;) — 463035818_is_not_an_ai, Feb 14 '19 at 21:28
I agree. The accepted answer on the duplicate is not the best answer. There are several other ones in that that are much better. — drescherjm, Feb 14 '19 at 21:28
In the other two links I cannot see the explicitly how is the "delete" command used in the main program. Here I fully understood how stuff works! thanks a lot! — Andreas Hadjigeorgiou, Feb 14 '19 at 21:31

Spinkoo · Answer 1 · 2019-02-14T21:17:18.403

0

1-Calling delete will mark the memory area as free. It won't necessary reset its old value.

2-Accessing freed memory will surely cause you an undefined behavior so that's extremely inadvisable thing to try

edited Feb 14 '19 at 21:17

answered Feb 14 '19 at 21:14

Spinkoo

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score 0 · Accepted Answer · answered Feb 14 '19 at 21:17

Always delete what you create with the new keyword. If you create an array of pointers using new keyword, use delete[] to delete all the pointer elements of the array.

how can I delete the objects if not like this?

This is the correct way of deleting the objects created with new keyword.

why do I get the value 28 after I used the command?

You should not deference a pointer after it is deleted. it results in an undefined behavior. You may get the old value or a nasty segmentation fault.

How to deallocate the dynamically allocated classes?

2 Answers2