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 if ( NULL == p ) {   // do stuff } 

How do I do the above for iterators? Is it possible at all?

#include <iostream> #include <list>  int main () {     std::list<int>::iterator it;    if ( NULL == it ) // this fails   {       std::cout<<"do stuff" << std::endl;   } } 

Answer 1

I managed to find this in the current standard (c++03 ). 24.1 p 5 tells :

Just as a regular pointer to an array guarantees that there is a pointer value pointing past the last element of the array, so for any iterator type there is an iterator value that points past the last element of a corresponding container. These values are called past-the-end values. Values of an iterator i for which the expression *i is defined are called dereferenceable. The library never assumes that past-the-end values are dereferenceable. Iterators can also have singular values that are not associated with any container. [Example: After the declaration of an uninitialized pointer x (as with int* x;), x must always be assumed to have a singular value of a pointer. ] Results of most expressions are undefined for singular values; the only exception is an assignment of a non-singular value to an iterator that holds a singular value. In this case the singular value is overwritten the same way as any other value. Dereferenceable values are always non- singular.

(Emphasis mine)

So the answer is : no, it is not possible.