Question

What will exactly happen if a member function try to do delete this;, like in the constructor of the following class?

class A
{
public:
    A(int);
    ~A();
    int *pi;
}

A::A(int i)
{
    delete this;
    pi = new int(i);
}

A::~A()
{
    delete pi;
}

Answer 1

This C++ FAQ entry answers this quite nicely, repeating here:

As long as you’re careful, it’s OK for an object to delete this.

Here’s how I define "careful":

• You must be absolutely 100% positively sure that this object was allocated via new (not by new[], nor by placement new, nor a local object on the stack, nor a global, nor a member of another object; but by plain ordinary new).
• You must be absolutely 100% positively sure that your member function will be the last member function invoked on this object.
• You must be absolutely 100% positively sure that the rest of your member function (after the delete this line) doesn’t touch any piece of this object (including calling any other member functions or touching any data members).
• You must be absolutely 100% positively sure that no one even touches the this pointer itself after the delete this line. In other words, you must not examine it, compare it with another pointer, compare it with NULL, print it, cast it, do anything with it.

You are violating the #3 by accessing pi after delete this