Question

How come this compiles and works:

class MyObject {
public:
  MyObject() {}
};

struct ItemGood {
  int Number;
  MyObject *Object;

  ItemGood(int Number, MyObject *Object) {
    this->Number = Number;
    this->Object = Object;
  }
};

const ItemGood ItemGoodList[] =
{
  { 0, new MyObject() },
  { 1, new MyObject() }
};

And this does not compile at all:

class MyObject {
public:
  MyObject() {}
};

struct ItemBad {
  int Number;
  std::auto_ptr<MyObject> AutoObject;

  ItemBad(int Number, MyObject *Object) {
    this->Number = Number;
    AutoObject = std::auto_ptr<MyObject>(Object);
  }
};

const ItemBad ItemBadList[] =
{
  { 0, new MyObject() },
  { 1, new MyObject() }
};

The error the compiler spits out is:

no matching function for call to ‘ItemBad::ItemBad(ItemBad)

I do not understand why something is trying to call that constructor, I don’t understand what is actually happening in this initializer list.

Answer 1

Because std::auto_ptr does not have a proper copy constructor, which means your class does not have a proper copy constructor, which means that it cannot be constructed from a temporary- which is what you’re trying to do.

Just junk auto_ptr and move to unique_ptr.