// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p255.cpp(120)9.4 Local class declarations [class.local]  "

#include <iostream>
int x;
void f() {
  static int s ;
  int x;
  const int N = 5;
  extern int q();
  struct local {
    int g() { return x; } // error: odr-use of automatic variable x
    int h() { return s; } // OK
    int k() { return ::x; } // OK
    int l() { return q(); } // OK
    int m() { return N; } // OK: not an odr-use
    int* n() { return &N; } // error: odr-use of automatic variable N
  };
}
local* p = 0; // error: local not in scope

int main(){
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p255
$ clang++ p255.cpp
p255.cpp:13:18: error: reference to local variable 'x' declared in enclosing function 'f'
int g() { return x; } // error: odr-use of automatic variable x
                 ^
p255.cpp:9:5: note: 'x' declared here
int x;
    ^
p255.cpp:18:19: error: cannot initialize return object of type 'int *' with an rvalue of type 'const int *'
int* n() { return &N; } // error: odr-use of automatic variable N
                  ^~
p255.cpp:21:1: error: unknown type name 'local'
local* p = 0; // error: local not in scope
^
3 errors generated.

$ g++-7 p255.cpp
p255.cpp: In member function 'int f()::local::g()':
p255.cpp:13:18: error: use of local variable with automatic storage from containing function
 int g() { return x; } // error: odr-use of automatic variable x
                  ^
p255.cpp:9:5: note: 'int x' declared here
 int x;
     ^
p255.cpp: In member function 'int* f()::local::n()':
p255.cpp:18:20: error: lvalue required as unary '&' operand
 int* n() { return &N; } // error: odr-use of automatic variable N
                    ^
p255.cpp: At global scope:
p255.cpp:21:1: error: 'local' does not name a type
 local* p = 0; // error: local not in scope
 ^~~~~

// N4606 Committee Draft, Standard for Programming Language C++
// http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/n4606.pdf 
#define msg "p255.cpp(120)9.4 Local class declarations [class.local]  "

#include <iostream>
int x;
void f() {
  static int s ;
  int x;
  const int N = 5;
  extern int q();
  struct local {
//    int g() { return x; } // error: odr-use of automatic variable x
    int h() { return s; } // OK
    int k() { return ::x; } // OK
    int l() { return q(); } // OK
    int m() { return N; } // OK: not an odr-use
//    int* n() { return &N; } // error: odr-use of automatic variable N
  };
  std::cout<< "f()" << std::endl;
}
//local* p = 0; // error: local not in scope

int main(){
  f();
  std::cout<< msg << std::endl;
  return EXIT_SUCCESS;
}

$ ./cppgl17.sh p255-2
$ clang++ p255-2.cpp
f()
p255.cpp(120)9.4 Local class declarations [class.local]  

$ g++-7 p255-2.cpp
f()
p255.cpp(120)9.4 Local class declarations [class.local]