Can you call a constructor within a destructor, or vise vesa?

warrener · #1 10-Jun-2008, 21:24

folks, I came across questions about calling constructor or destructor.
I am curious whether you can:

Code:

1. call a constructor in a constructor
2. call a destructor in a constructor
3. call a constructor in a destructor
4. call a destructor in a destructor
5. call a constructor in a member function
6. call a destructor in a member function

So I wrote the following code and want to share with you what I got. Comments are welcomed! Please check if I miss anything.

1. call a constructor in a constructor

Code:

class A{
public: 
    A(){
        A();
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;
    ~A(){
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};
int main()
{
    A obj;
    return 0; 
}

Basically you are not actually calling the constructor, you are just generating a temp object.
If you use this->A() to call then you will get an error.

Code:

error: calling type `A' like a method

Also this brings a recursive calling. Soon you will use up memory and crash.

2. call a destructor in a constructor

Code:

class A{
public: 
    A(){
        this->~A();
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;
    ~A(){
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};

int main()
{
    A obj;
    return 0; 
}

You can't call ~A() without qualifying: this->~A(). At least I didn't figure out a way to avoid it.
Yes, you can call destructor in the class, and you can see it destructs the member variable x.

3. call a constructor in a destructor

Code:

class A{
public: 
    A(){
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;
    ~A(){
        A();
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};

int main()
{
    A obj;
    return 0; 
}

Again, you are not calling constructor, just a temp obj.

4. call a destructor in a destructor

Code:

class A{
public: 
    A(){
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;

    ~A(){
        this->~A();
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};

int main()
{
    A obj;
    return 0; 
}

This also gives you a dead loop.

5. call a constructor in a member function

Code:

class A{
public: 
    A(){
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;
    void foo()
    {
        cout<<"BEFORE foo"<<x<<endl;
        A();
        cout<<"AFTER foo"<<x<<endl;
    }
    ~A(){
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};

int main()
{
    A obj;
    obj.foo();
    return 0; 
}

It works. just a temp obj.

6. call a destructor in a member function

Code:

class A{
public: 
    A(){
        x = 100;
        cout<<"A() "<<x<<endl;
    }
    int x;
    void foo()
    {
        cout<<"BEFORE foo"<<x<<endl;
        A();
        cout<<"AFTER foo"<<x<<endl;
    }
    ~A(){
        x = 0;
        cout<<"~A() "<<x<<endl;
    }
};

int main()
{
    A obj;
    obj.foo();
    return 0; 
}

It works.

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