On Sat, 24 May 2025, 12:43 Frederick Virchanza Gotham via Std-Proposals, <
std-proposals_at_[hidden]> wrote:

> The Standard guarantees that the following containers' elements are
> stored in contiguous memory locations:
>
> basic_string
> vector
> array
> inplace_vector
>
> Therefore if you get the first element's address with:
>
> MyType *p = &mycontainer.front();
>
> Then you can simply add to it to get the elements that follow:
>
> MyType *p5 = p + 5;
>
> If you want to turn a valid iterator into a pointer, you can just do:
>
> auto it = mycontainer.begin();
> MyType *p = &*it;
>
> This will work fine on most computers and compilers, even if you
> dereference the 'end' iterator. But the Microsoft compiler won't allow
> it, nor will g++ or clang if you define _GLIBCXX_DEBUG. And strictly
> speaking, the Standard dictates that the behaviour is undefined.
>
> I think some implementations of the C++ standard library (e.g.
> Dinkumware, libstdc++) provide you with a function/method to turn a
> contiguous iterator into a pointer, but to my knowledge there is no
> standard way of doing this. I'm not aware of any papers to solve this
> problem -- but for all I know, maybe it snuck into C++26 without me
> noticing.
>
> Anyway what I'm saying is that the C++ standard library should provide
> a function/method to turn a contiguous iterator into a pointer, which
> can be used safely with an 'end' pointer. This could be a standalone
> function such as:
>
> auto it = mycontainer.end();
> MyType *p = std::contiguous_p(it);
>
> or perhaps a member function of the iterator class:
>
> auto it = mycontainer.end();
> MyType *p = it.to_pointer();
>
> There's no excuse for the Standard not providing this.
>

It already exists, std::to_address

Using &*it is wrong.