Is there a built-in way to cast to a different underlying type but preserve const qualifiers?

Question

Does the C++11/14/17 standard library have a way to cast an object to a different type but with the same cv-qualifiers as the original object? E. g.

char* ptr;
const char* cptr;

type_cast<void*>(ptr) should yield the type void*
type_cast<void*>(cptr) should yield the type const void*

Answer 1

Not in the standard library, but it is certainly possible to implement it yourself:

namespace detail_base_type_cast {
    template <class In, class Out>
    struct copy_cv {
        using type = Out;
    };

    template <class In, class Out>
    struct copy_cv<In const, Out &> {
        using type = Out const &;
    };

    template <class In, class Out>
    struct copy_cv<In volatile, Out &> {
        using type = Out volatile &;
    };

    template <class In, class Out>
    struct copy_cv<In const volatile, Out &> {
        using type = Out const volatile &;
    };
}

template <class Out, class In>
typename detail_base_type_cast::copy_cv<In, Out>::type
base_type_cast(In &obj) {
    return obj; // Implicit derived-to-base conversion
}