How to check if the iterator is initialized?

Question

If I use a default constructor for an iterator, how to check if it was assigned later on?

For pointers, I could do this :

int *p = NULL;
/// some code
         


        

Answer 1

Since there is no default value for iterators (like there is NULL for pointers), in situation where i need a common default value for a Object::iterator (before any actual Object has been created) I create a dummy static variable and use its ::end() as the default.

Update : This only works for Release, because in DEBUG (or with _HAS_ITERATOR_DEBUGGING=1) comparison operators check if both iterators point to the same object/container.

For example for vector I would do :

class A
{
public :
    A() :  myIterator1(dummyVector.end()), myIterator2(dummyVector.end()) {}
    // needed iterators
    vector::iterator myIterator1;
    vector::iterator myIterator2;

    static const vector dummyVector;
}

#define  IT_NULL A::dummyObject.end()

void maint() {
    A::dummyObject = vector(); // initialize the Null iterator

    A a;
    if(a.myIterator1 == IT_NULL) cout << "Iterator not yet initialized";
}