Is self-initialization 'A a = a;' allowed?

Question

This code fails at runtime in the copy constructor.
But the compiler (MSVS2008) issues no warnings.

Could you explain (preferably cite the standard) whether this

Answer 1

According to the standard (12.6.1 [class.expl.init] ) self initialization is perfectly legal.

Therefore the following is legal.

A a = a;

You just need to write your copy constructor to deal with it correctly.

A(const A& rv)
{
    if(&rv == this) {
        p = new int(0);
        return;
    }

    p = new int(*rv.p);
}

Edit: Updated code based on comments.

Answer 2

Interesting reading on self-assignment: http://www.gotw.ca/gotw/011.htm

In particular, note "Postscript #1" in relation to this question and some of the answers given.

Answer 3

A a = a; definitely should not be written. But a = a could be written. Your assignment operator must check for &rv == this and do nothing in case of a self-copy.

Oh, yes, you do need to write an assignment operator for class A.

Answer 4

Your code is not calling the standard constructor but the copy constructor, so you are accessing an uninitialized pointer.