| //===----------------------------------------------------------------------===// |
| // |
| // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. |
| // See https://llvm.org/LICENSE.txt for license information. |
| // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #ifndef _LIBCPP___TYPE_TRAITS_DATASIZEOF_H |
| #define _LIBCPP___TYPE_TRAITS_DATASIZEOF_H |
| |
| #include <__config> |
| #include <__type_traits/is_class.h> |
| #include <__type_traits/is_final.h> |
| #include <cstddef> |
| |
| #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER) |
| # pragma GCC system_header |
| #endif |
| |
| // This trait provides the size of a type excluding any tail padding. |
| // |
| // It is useful in contexts where performing an operation using the full size of the class (including padding) may |
| // have unintended side effects, such as overwriting a derived class' member when writing the tail padding of a class |
| // through a pointer-to-base. |
| |
| _LIBCPP_BEGIN_NAMESPACE_STD |
| |
| template <class _Tp> |
| struct __libcpp_datasizeof { |
| #if __has_cpp_attribute(__no_unique_address__) |
| template <class = char> |
| struct _FirstPaddingByte { |
| [[__no_unique_address__]] _Tp __v_; |
| char __first_padding_byte_; |
| }; |
| #else |
| template <bool = __libcpp_is_final<_Tp>::value || !is_class<_Tp>::value> |
| struct _FirstPaddingByte : _Tp { |
| char __first_padding_byte_; |
| }; |
| |
| template <> |
| struct _FirstPaddingByte<true> { |
| _Tp __v_; |
| char __first_padding_byte_; |
| }; |
| #endif |
| |
| static const size_t value = offsetof(_FirstPaddingByte<>, __first_padding_byte_); |
| }; |
| |
| _LIBCPP_END_NAMESPACE_STD |
| |
| #endif // _LIBCPP___TYPE_TRAITS_DATASIZEOF_H |