C++11 private default constructor

Question

The following C++11 code compiles successfully on my GCC 4.8:

struct NonStack
{
private:
  NonStack() = default;
public:
  static NonStack* Create(){
    return new NonStack;
  }
};
NonStack a;

int main() { }

However the following gives a compilation error:

struct NonStack
{
private:
  NonStack(){}
};

NonStack a; 

int main() { }

Why does the first one succeed? Shouldn't the private defaulted constructor prohibit creation of an object via NonStack a;?

Answer 1

This is gcc bug 54812, the compiler fails to respect access specifiers for explicitly defaulted special member functions. Bug 56429, which is marked as a duplicate of the earlier one, has a test case that is almost identical to the example in the question.

The solutions are to upgrade to gcc4.9, which resolves the issue. Or create an empty body for the constructor, instead of explicitly defaulting it, as you've done in the second example.