c++ - Why do we need to use virtual ~A() = default; instead of virtual ~A() {} in C++11? -

In the stack overflow post , I have the comment:

In C +11 you really want to do virtual ~ A () = default; Otherwise, you will lose the alleged driver.

virtual ~ A () = what is default; For ? Virtual ~ A () {} ?

The comment is not correct.

both:

  virtual ~ a () = default;   
 and  
  virtual_a () {}   
 user  declared . And inhibit members of the inactive conduction if the destroyer user is declared.  
 [dcl.fct.def.default] / p4  User declared  and  User provided  Special member:  
 
 A special member function is  provided by the user  if it has been declared by the user and clearly not declared in the previous announcement or has been removed. / P>