C++ code - 9 lines

Link:

C++, pasted on Nov 19:

struct A {
  A(int);  // prevent default ctor
};

struct B {
  A a;
};

B b;

Output:

1
2
3

t.cpp: In constructor 'B::B()':
Line 5: error: no matching function for call to 'A::A()'
compilation terminated due to -Wfatal-errors.