Return error when returning a reference

Question

A function returns a reference on int

int&     MyClass::getElement(int position)
{
   if (position < _size)
      return (_array[position]);
   return ([...]) // An Error
}

My first think was to return NULL. But obviously a reference can not be NULL.

What is the right way to return an error in this case?

Answer 1

Various options, roughly ordered with my preferred options first:

• Throw an exception, conventionally std::out_of_range
• Return a pointer
• Return some other type with a well-define invalid value, like std::pair<bool,int&> or boost::optional<int&>. This is more useful if you want to return something by value, not reference, so can't return a pointer.
• Return a reference to a static magic number, if you can choose a number which will never be valid data. This is nasty since there's nothing to stop the caller from modifying it.