STL vector erase via pointer

Question

I understand (at least I think I do) that pointers can be used as random STL iterators.

Why does the following code not compile unless I cast the pointer to an iterator?

vector<int> v{1, 2, 3};
v.erase(&v[0]);

Answer 1

You can pass pointers to algorithms like std::sort, std::find, or std::copy. These are templates that are configurable for anything that works as an appropriate iterator.

This does not mean that different iterators necessarily convert to each other.

The method erase of the std::vector<int> container can only work with iterators to elements of the same vector. As has been pointed out this may be implemented as a pointer, but it usually is not, for reasons stated here: C++ std::vector<>::iterator is not a pointer, why?

Consider std::find:

template< class InputIt, class T >
InputIt find( InputIt first, InputIt last, const T& value );

Here InputIt is a template parameter. The template std::find will work with any iterator type that fulfills the requirements of an input iterator, and whose operator* returns something that can be compared to type T. Pointers work well here. As Fire Lancer pointed out correctly in a comment, both first and last must be of type InputIt.

Now compare this to std::vector::erase:

iterator erase( const_iterator pos );

This takes a const_iterator, which is one of the typedefs of the std::vector class. This is one particular type of iterator, not a template parameter.

Answer 2

The definition of vector.erase(...) is

iterator erase( const_iterator pos );

The const iterator is a class in itself. So if there was a conversion of a plain pointer to this class, then this could be done. But I don't think there is any.

But one thing is to use it in a place where an iterator is expected, and another is to use in algorithms.

Where an iterator is required, only a iterator can be used.

In algorithms, an iterator is not expected. Only a object for which a Concept of an iterator is satisified (usually a begin and end return the required iterator/pointer).