// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p301.cpp(145)12.7 Construction and destruction [class.cdtor]"
// Edited by Dr. Ogawa Kiyoshi. Compile procedure and results record.

#include <iostream>

struct X { int i; };
struct Y : X { Y(); }; // non-trivial
struct A { int a; };
struct B : public A { int j; Y y; }; // non-trivial
extern B bobj;
B* pb = &bobj; // OK
int* p1 = &bobj.a; // undefined, refers to base class member
int* p2 = &bobj.y.i; // undefined, refers to member’s member
A* pa = &bobj; // undefined, upcast to a base class type
B bobj; // definition of bobj
extern X xobj;
int* p3 = &xobj.i; //OK, X is a trivial class
X xobj;

struct W { int j; };
struct X1 : public virtual W { };
struct Y1 {
int* p;
X1 x;
Y1() : p(&x.j) { // undefined, x is not yet constructed
}
};

struct A2 { };
struct B2 : virtual A2 { };
struct C2 : B2 { };
struct D2 : virtual A2 { D2(A2*); };
struct X2 { X2(A2*); };
struct E2 : C2, D2, X2 {
E2() : D2(this), // undefined: upcast from E* to A*
// might use path E2* ! D2* ! A2*
// but D2 is not constructed
// D2((C2*)this), // defined:
// E2* ! C2* defined because E2() has started
// and C2* ! A2* defined because
// C2 fully constructed
X2(this) { // defined: upon construction of X,
// C2/B2/D2/A2 sublattice is fully constructed
}
};

struct V {
virtual void f();
virtual void g();
};
struct A3 : virtual V {
virtual void f();
};
struct B3 : virtual V {
virtual void g();
B3(V*, A3*);
};
struct D3 : A3, B3 {
virtual void f();
virtual void g();
D3() : B3((A3*)this, this) { }
};
B3::B3(V* v, A3* a) {
f(); // calls V::f, not A3::f
g(); // calls B3::g, not D3::g
v->g(); // v is base of B, the call is well-defined, calls B3::g
a->f(); // undefined behavior, a’s type not a base of B3
}

struct V4 {
virtual void f();
};
struct A4 : virtual V4 { };
struct B4 : virtual V4 {
B4(V4*, A4*);
};
struct D4 : A4, B4 {
D4() : B4((A4*)this, this) { }
};
B4::B4(V4* v, A4* a) {
typeid(*this); // type_info for B4
typeid(*v); // well-defined: *v has type V4, a base of B4
// yields type_info for B4
typeid(*a); // undefined behavior: type A4 not a base of B4
dynamic_cast<B4*>(v); // well-defined: v of type V4*, V4 base of B4
// results in B4*
dynamic_cast<B4*>(a); // undefined behavior,
// a has type A4*, A4 not a base of B4
}
int main(){
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p301
$ clang++ p301.cpp
p301.cpp:83:1: warning: expression result unused [-Wunused-value]
typeid(*this); // type_info for B4
^~~~~~~~~~~~~
p301.cpp:84:1: warning: expression result unused [-Wunused-value]
typeid(*v); // well-defined: *v has type V4, a base of B4
^~~~~~~~~~
p301.cpp:86:1: warning: expression result unused [-Wunused-value]
typeid(*a); // undefined behavior: type A4 not a base of B4
^~~~~~~~~~
p301.cpp:87:1: warning: expression result unused [-Wunused-value]
dynamic_cast<B4*>(v); // well-defined: v of type V4*, V4 base of B4
^~~~~~~~~~~~~~~~~~~~
p301.cpp:89:1: warning: expression result unused [-Wunused-value]
dynamic_cast<B4*>(a); // undefined behavior,
^~~~~~~~~~~~~~~~~~~~
5 warnings generated.
Undefined symbols for architecture x86_64:
  "Y::()", referenced from:
      B::() in p301-9b2046.o
  "V4::f()", referenced from:
      vtable for B4 in p301-9b2046.o
  "typeinfo for V4", referenced from:
      B4::B4(V4*, A4*) in p301-9b2046.o
      B4::B4(V4*, A4*) in p301-9b2046.o
      typeinfo for B4 in p301-9b2046.o
      typeinfo for A4 in p301-9b2046.o
  "vtable for V", referenced from:
      V::() in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for B3", referenced from:
      B3::B3(V*, A3*) in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for V4", referenced from:
      V4::V4() in p301-9b2046.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang-6.0: error: linker command failed with exit code 1 (use -v to see invocation)

$ g++-7 p301.cpp
Undefined symbols for architecture x86_64:
  "V::f()", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
      B3::B3(V*, A3*)   in ccqdeMPa.o
  "Y::Y()", referenced from:
      B::B()     in ccqdeMPa.o
  "B3::g()", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
      B3::B3(V*, A3*)   in ccqdeMPa.o
  "V4::f()", referenced from:
      vtable for B4 in ccqdeMPa.o
  "typeinfo for V4", referenced from:
      typeinfo for B4 in ccqdeMPa.o
      typeinfo for A4 in ccqdeMPa.o
  "vtable for V", referenced from:
      V::V()     in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for B3", referenced from:
      B3::B3(V*, A3*)   in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
  "vtable for V4", referenced from:
      V4::V4()    in ccqdeMPa.o
  NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status