My C++ Quiz

Question #47: Which, if any, of the member function definitions below are ill-formed?
53% on 887 times asked

#include <iostream>

int g_x = 44; 

struct Foo 
{ 
  int m_x; 

  static int s_x; 

  Foo(int x) : m_x(x) {} 

  int a(int x = g_x) 
  { 
    return x + 1; 
  } 

  int b(int x = m_x) 
  { 
    return x + 1; 
  } 

  int c(int x = s_x) 
  { 
    return x + 1; 
  } 
}; 

int Foo::s_x = 22; 

int main(int argc, char** argv) 
{ 
  Foo f(6); 

  std::cout << f.a() << std::endl; 
  std::cout << f.b() << std::endl; 
  std::cout << f.c() << std::endl; 

  return 0; 
}