[support.types.layout] (original) (raw)

17 Language support library [support]

17.2 Common definitions [support.types]

17.2.4 Sizes, alignments, and offsets [support.types.layout]

The macrooffsetof(type, member-designator)has the same semantics as the corresponding macro in the C standard library header , but accepts a restricted set of _type_arguments in this document.

Use of the offsetof macro with a _type_other than a standard-layout class ([class.prop]) is conditionally-supported.152

The expression offsetof(type, member-designator)is never type-dependent and it isvalue-dependent if and only if type is dependent.

The result of applying the offsetof macro to a static data member or a function member is undefined.

No operation invoked by the offsetof macro shall throw an exception andnoexcept(offsetof(type, member-designator)) shall be true.

The type ptrdiff_t is animplementation-defined signed integer type that can hold the difference of two subscripts in an array object, as described in [expr.add].

The type size_t is animplementation-defined unsigned integer type that is large enough to contain the size in bytes of any object ([expr.sizeof]).

Recommended practice: An implementation should choose types for ptrdiff_t and size_twhose integer conversion ranks ([conv.rank]) are no greater than that ofsigned long int unless a larger size is necessary to contain all the possible values.

The typemax_align_t is a trivially copyable standard-layout type whose alignment requirement is at least as great as that of every scalar type, and whose alignment requirement is supported in every context ([basic.align]).

std::is_trivially_default_constructible_v<max_align_t> is true.