std::to_address

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Defined in header`<memory>`
template<class Ptr> constexprauto to_address(const Ptr& p)noexcept;	(1)	(since C++20)
template<class T> constexpr T* to_address( T* p)noexcept;	(2)	(since C++20)

Obtain the address represented byp without forming a reference to the object pointed to byp.

1)Fancy pointer overload: If the expressionstd::pointer_traits<Ptr>::to_address(p) is well-formed, returns the result of that expression. Otherwise, returnsstd::to_address(p.operator->()).

2) Raw pointer overload: IfT is a function type, the program is ill-formed. Otherwise, returnsp unmodified.

[edit]Parameters

fancy or raw pointer

[edit]Return value

Raw pointer that represents the same address asp does.

[edit]Possible implementation

template<class T>constexpr T* to_address(T* p)noexcept{    static_assert(!std::is_function_v<T>);return p;} template<class T>constexprauto to_address(const T& p)noexcept{ifconstexpr(requires{std::pointer_traits<T>::to_address(p);})returnstd::pointer_traits<T>::to_address(p);elsereturn std::to_address(p.operator->());}

[edit]Notes

std::to_address can be used even whenp does not reference storage that has an object constructed in it, in which casestd::addressof(*p) cannot be used because there is no valid object for the parameter ofstd::addressof to bind to.

The fancy pointer overload ofstd::to_address inspects thestd::pointer_traits<Ptr> specialization. If instantiating that specialization is itself ill-formed (typically becauseelement_type cannot be defined), that results in a hard error outside the immediate context and renders the program ill-formed.

std::to_address may additionally be used on iterators that satisfystd::contiguous_iterator.

Feature-test macro	Value	Std	Feature
`__cpp_lib_to_address`	`201711L`	(C++20)	Utility to convert a pointer to a raw pointer (`std::to_address`)

[edit]Example

Run this code

#include <memory> template<class A>auto allocator_new(A& a){auto p= a.allocate(1);try{std::allocator_traits<A>::construct(a, std::to_address(p));}catch(...){        a.deallocate(p,1);throw;}return p;} template<class A>void allocator_delete(A& a,typenamestd::allocator_traits<A>::pointer p){std::allocator_traits<A>::destroy(a, std::to_address(p));    a.deallocate(p,1);} int main(){std::allocator<int> a;auto p= allocator_new(a);    allocator_delete(a, p);}

[edit]See also

pointer_traits (C++11)	provides information about pointer-like types (class template)[edit]
to_address [static](C++20)(optional)	obtains a raw pointer from a fancy pointer (inverse of`pointer_to`) (public static member function of`std::pointer_traits<Ptr>`)[edit]