c++ - To use shared_ptr, is it safe ? -

i have got confused shared_ptr.

say, have classes:

class foo {      int _f; }; typedef std::shared_ptr<foo> fooptr;  class bar {     int _b; }; typedef std::shared_ptr<bar> barptr;  class foobar : public foo, public bar {     int _fb; };  int main () {      foobar *fb1 = new foobar();     foobar *fb2 = new foobar();      fooptr f((foo *)fb1);     barptr b((bar *)fb2);      return 0; } 

because b.get() != fb2, should crash when program exit? or safe ?

a shared_ptr<base> can safely take ownership of derived*, if base not have virtual destructor.

however, works if shared_ptr knows derived type of object when takes ownership of it. if remove casts

fooptr f(fb1); fooptr b(fb2); 

then you'd okay. casts, shared_ptr cannot know most-derived type of object when takes ownership of it, behavior undefined, if had said:

foo* f = new foobar(); delete f; 

the best thing follow rule "a base class destructor should either public , virtual, or protected , nonvirtual."