What is the order in which the destructors and the constructors are called in C++

Question

What is the order in which the destructors and the constructors are called in C++? Using the examples of some Base classes and Derived Classes

Answer 1

The order is:

Base constructor

Derived constructor

Derived destructor

Base destructor

Example:

class B
{
public:
  B()
  {  
    cout<<"Construct B"<<endl;
  }

  virtual ~B()
  {
    cout<<"Destruct B"<<endl;
  }
};

class D : public B
{
public:
  D()
  {  
    cout<<"Construct D"<<endl;
  }

  virtual ~D()
  {
    cout<<"Destruct D"<<endl;
  }
};



int main(int argc, char **argv)
{
  B b; 
  return 0;
}

Output of example:

Construct B

Construct D

Destruct D

Destruct B

Multiple levels of inheritance works like a stack:

If you consider pushing an item onto the stack as construction, and taking it off as destruction, then you can look at multiple levels of inheritance like a stack.

This works for any number of levels.

Example D2 derives from D derives from B.

Push B on the stack, push D on the stack, push D2 on the stack. So the construction order is B, D, D2. Then to find out destruction order start popping. D2, D, B

More complicated examples:

For more complicated examples, please see the link provided by @JaredPar

Answer 2

A detailed description of these events, including virtual and multiple inheritance is available at the C++ FAQ Lite. Section 25.14 and 25.15

http://www.parashift.com/c++-faq-lite/multiple-inheritance.html#faq-25.14

Answer 3

Also, keep in mind that while array elements are constructed first -> last, they are destructed in the reverse order: last -> first.