the location of delete in the class to delete pointer data member

Question

I write a simple class, I just wanna know where I should delete my pointer.

#include<iostream>


class test
{
private:
    int* sum{new int};


public:
    int addFunc(int num1 = 5, int num2 = 2)
    {
        *sum = num1 + num2;
        return *sum;
    }

    void print()
    {
        std::cout << *sum << std::endl;
    }

};

int main()
{
    test obj;
    obj.addFunc();
    obj.print();
}

I know how to use unique pointers to get rid of deleting pointers, should I delete my pointer after returning it or somewhere else.

do you also know how to use objects to get rid of pointers altogether? Why do you use a pointer here? — 463035818_is_not_a_number, Mar 09 '20 at 09:48
https://stackoverflow.com/questions/6500313/why-should-c-programmers-minimize-use-of-new — 463035818_is_not_a_number, Mar 09 '20 at 09:48
Logically: in destructor. Generally: before the program exits. Specifically: anywhere you need to. — Daniel Langr, Mar 09 '20 at 09:49
and dont forget the single responsibility principle. Managing a resource is already a responsibility, and adding two numbers is another. If the member `sum` needs to be a dynamically allocated `int` then memory managment should be wrapped in a container/smart pointer — 463035818_is_not_a_number, Mar 09 '20 at 09:50
You're not returning a pointer anywhere. If you're thinking of `return *sum;`, that's returning the value of the `int` that `sum` points to, not the pointer `sum`. — molbdnilo, Mar 09 '20 at 10:12

score 3 · Accepted Answer · answered Mar 09 '20 at 09:58

You delete it in the destructor. But if you're managing raw memory you'll also have to implement a suitable copy constructor & copy assignment operator and their move counterparts.

In 99%+ of these cases you'll just want to use automatic lifetime or smart pointers instead.

score 2 · Answer 2 · answered Mar 09 '20 at 10:04

Short answer: never, meaning at program end.

The problem is that your class is copyable. If you delete the pointer in destructor (which would be the correct place for something allocated at construction time), you will get a dangling pointer in the following use case:

you pass a reference to a test object to a function
inside that function you copy the object to a local object: the pointer will be copied so both the original object and the local copy will point the the same int
at the end the the function, the local object will be destroyed. If if deletes the int, the original will get a dangling pointer.

Long story made short: as soon as you use allocation at construction time, you should care for the copy/move construction and assignment, and destruction.

the location of delete in the class to delete pointer data member

2 Answers2