libstdc++-v3/testsuite/23_containers/span/layout_compat.cc

   1 // Copyright (C) 2020-2025 Free Software Foundation, Inc.
   2 //
   3 // This file is part of the GNU ISO C++ Library.  This library is free
   4 // software; you can redistribute it and/or modify it under the
   5 // terms of the GNU General Public License as published by the
   6 // Free Software Foundation; either version 3, or (at your option)
   7 // any later version.
   8
   9 // This library is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13
  14 // You should have received a copy of the GNU General Public License along
  15 // with this library; see the file COPYING3.  If not see
  16 // <http://www.gnu.org/licenses/>.
  17
  18 // { dg-do compile { target c++20 } }
  19
  20 #include <span>
  21 #include <cstddef>
  22
  23 #if __has_include(<sys/uio.h>)
  24 #include <sys/uio.h>
  25 #else
  26 struct iovec { void* iov_base; std::size_t iov_len; };
  27 #endif
  28
  29 // std::span cannot possibly be layout-compatible with struct iovec because
  30 // iovec::iov_base is a void* and span<void> is ill-formed. Additionally,
  31 // the libstdc++ std::span uses [[no_unique_address]] on the second member,
  32 // so that it's not present for a span of static extent, and that affects
  33 // layout-compatibility too.
  34 // Use this to check the size and alignment are compatible.
  35 template<typename T, typename U>
  36   constexpr bool same_size_and_alignment
  37     = std::is_standard_layout_v<T> && std::is_standard_layout_v<U>
  38       && sizeof(T) == sizeof(U) && alignof(T) == alignof(U);
  39
  40 void
  41 test_pr95609()
  42 {
  43   using rbuf = std::span<const std::byte>;
  44   static_assert(same_size_and_alignment<rbuf, struct iovec>);
  45
  46   using wbuf = std::span<std::byte>;
  47   static_assert(same_size_and_alignment<wbuf, struct iovec>);
  48 }