const reference to temporary oddity

Question

We all know that things like this are valid in c++:

const T &x = T();

while:

T &x = T();

is not.<

Answer 1

It prints 10 every time.

Modify the main function a little and it won't print 10 anymore:

int main()
{
    B* p = f();
    cout << "C++\n";   // prints C++
    p->b();            // prints 4077568
}

how does this link gets established at what level?

See 12.2 [class.temporary] §4 and §5:

Temporary objects are destroyed as the last step in evaluating the full-expression that (lexically) contains the point where they were created.

There are two contexts in which temporaries are destroyed at a different point than the end of the full-expression. The first context is [...]

The second context is when a reference is bound to a temporary. The temporary to which the reference is bound or the temporary that is the complete object of a subobject to which the reference is bound persists for the lifetime of the reference except: [...]

A temporary bound to a reference parameter in a function call persists until the completion of the full-expression containing the call.

So in your case, the temporary is destroyed after the evaluation of the full-expression new B(A(10)).