Question

In continuation to my previous question, I would like to ask the following :

Given a C++ function having a new statement in it but not returning anything explicitly (i.e. with a return statement), should it also always have a delete?

If no, could you please give me an example.

Answer 1

It doesn’t have to explicitly return the newly-created object, but it should pass it to something else in some way. Possible scenarios include:

• In a member function, create an object and assign it to a field of the containing object.

Example:

class Foo {
    private:
        Baz* baz;
    public:
        Foo() : baz(0) { }
        void create_bar() { baz = new Baz(); }
        ~Foo() { delete baz; }
};

• Passing the new object to something else.

Examples:

void foo() {
    // assuming bar lives in the global scope
    bar.baz = new Baz();
}

void foo2(Bar& bar) {
    bar.baz = new Baz();
    // or, better:
    bar.setBaz(new Baz());
}

• Using some kind of garbage-collecting pointer type.

Example:

std::auto_ptr<Baz> foo() {
    return new Baz();
}

• Passing the pointer into another function that does something with it and then deletes it.

Example:

void foo(Bar* bar) {
    bar->dostuff();
    delete bar;
}

void baz() {
    Bar* bar = new Bar();
    foo(bar);
}