some question about vector

You can not compare iterators to NULL (or iterators to other container objects). It was possible in VS2003 only because it (i. e. VS2003) wasn't conform to the standard, but in newer versions (and in the C++ standard) such comparisons are illegal, or at the very least undefined.

You can compare iterators only if they point to the same container object. it is not sufficient they are of the same type. Because of this dependency to the actual object, the error can not be caught at compile time, therefore the implementation contains an assertion that will alert you at runtime.

If you want to test an iterator to see whether it has reached the end of the container, then you must create an iterator constant that represents exactly that:

void Foo()
   std::vector<int> va;
   std::vector<int> vb;
   std::vector<int>::iterator it_va = va.begin();
   std::vector<int>::iterator va_end = va.end();
   if (it_va == va_end) // ok
      std::cout << "end of vector a" << std::endl;
   std::vector<int>::iterator it_vb = vb.begin();
   std::vector<int>::iterator vb_end = vb.end();
   if (it_vb == vb_end) // ok
      std::cout << "end of vector b" << std::endl;

   if (it_vb == va_end) // error!
      std::cout "something wonderful has happened ..." << std::endl;
}

In response to your question in solution 2, the way you find out if your iterator is valid or not, is by comparing it to the iterator returned by the end() member function of the container. The end() iterator is comparable to NULL for stl containers. You cannot dereference this iterator, the results are similar to trying to dereference a NULL pointer.

In the original code, if you wanted to print out the message if the iterator was not valid, or as you were asking, NULL or empty, this is what it would look like:

        vector<edssmsreftable_t> a;
// Don't need this anymore, cannot compare iterators from two different containers
//        vector<edssmsreftable_t> b;
 
	a.push_back(EdsSmsRefTable_t(10));
	vector<edssmsreftable_t>::iterator begin = a.begin();
 
	if (begin == a.end())
        {    
          // The iterator is the same as the end iterator.
          // That means you are at the end of the container.
          ... 
        }
</edssmsreftable_t></edssmsreftable_t></edssmsreftable_t>

Alternatively, if you just wanted to check if your container is empty, use the empty() member function of the stl container.

Hi,

I don't understand what you mean by the following line.

if (begin == b.begin())


If you are hoping to compare the two vector elements , this is not the right way. You need to create an iterator, Then traverse the entire list and compare each elements.