Question

lets say I have

class : foo
{
  public:
  static const foo Invalidfoo;
  foo();
  foo(int, string);
  private:
  int number;
  std::string name;
};

Is it safe or prone to any problem?

EDIT :

I want to use this to have an invalid object to return as a reference to launch errors.

Answer 1

It is perfectly legal, but the following is better:

class foo:
{
public:
    static const& foo Invalidfoo()
    {
        static foo Invalidfoo_;
        return Invalidfoo_;
    }

private:
      foo();
};

This way you are guaranteed that the object is initialized the first time it is used.

Edit: But no matter how you do it, you still have a global object, and that can be a cause of problem. The best solution may be to call the default constructor each time you need a default constructed object. In terms of efficiency, the difference is probably negligable.