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The C and C++ Include Header Files

cat -n /usr/include/c++/15/ext/aligned_buffer.h

     1	// Aligned memory buffer -*- C++ -*-
     2	
     3	// Copyright (C) 2013-2025 Free Software Foundation, Inc.
     4	//
     5	// This file is part of the GNU ISO C++ Library.  This library is free
     6	// software; you can redistribute it and/or modify it under the
     7	// terms of the GNU General Public License as published by the
     8	// Free Software Foundation; either version 3, or (at your option)
     9	// any later version.
    10	
    11	// This library is distributed in the hope that it will be useful,
    12	// but WITHOUT ANY WARRANTY; without even the implied warranty of
    13	// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    14	// GNU General Public License for more details.
    15	
    16	// Under Section 7 of GPL version 3, you are granted additional
    17	// permissions described in the GCC Runtime Library Exception, version
    18	// 3.1, as published by the Free Software Foundation.
    19	
    20	// You should have received a copy of the GNU General Public License and
    21	// a copy of the GCC Runtime Library Exception along with this program;
    22	// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
    23	// <http://www.gnu.org/licenses/>.
    24	
    25	/** @file ext/aligned_buffer.h
    26	 *  This file is a GNU extension to the Standard C++ Library.
    27	 */
    28	
    29	#ifndef _ALIGNED_BUFFER_H
    30	#define _ALIGNED_BUFFER_H 1
    31	
    32	#ifdef _GLIBCXX_SYSHDR
    33	#pragma GCC system_header
    34	#endif
    35	
    36	#if __cplusplus >= 201103L
    37	# include <type_traits>
    38	#else
    39	# include <bits/c++0x_warning.h>
    40	#endif
    41	
    42	namespace __gnu_cxx
    43	{
    44	  // A utility type containing a POD object that can hold an object of type
    45	  // _Tp initialized via placement new or allocator_traits::construct.
    46	  // Intended for use as a data member subobject, use __aligned_buffer for
    47	  // complete objects.
    48	  template<typename _Tp>
    49	    struct __aligned_membuf
    50	    {
    51	      // Target macro ADJUST_FIELD_ALIGN can produce different alignment for
    52	      // types when used as class members. __aligned_membuf is intended
    53	      // for use as a class member, so align the buffer as for a class member.
    54	      // Since GCC 8 we can just use alignas(_Tp) to get the right alignment.
    55	#ifdef __EDG__
    56	      // The EDG front end does not implement the PR c++/69560 alignof change.
    57	      struct _Tp2 { _Tp _M_t; };
    58	      alignas(__alignof__(_Tp2::_M_t))
    59	#else
    60	      alignas(_Tp)
    61	#endif
    62		unsigned char _M_storage[sizeof(_Tp)];
    63	
    64	      __aligned_membuf() = default;
    65	
    66	      // Can be used to avoid value-initialization zeroing _M_storage.
    67	      __aligned_membuf(std::nullptr_t) { }
    68	
    69	      void*
    70	      _M_addr() noexcept
    71	      { return static_cast<void*>(&_M_storage); }
    72	
    73	      const void*
    74	      _M_addr() const noexcept
    75	      { return static_cast<const void*>(&_M_storage); }
    76	
    77	      _Tp*
    78	      _M_ptr() noexcept
    79	      { return static_cast<_Tp*>(_M_addr()); }
    80	
    81	      const _Tp*
    82	      _M_ptr() const noexcept
    83	      { return static_cast<const _Tp*>(_M_addr()); }
    84	    };
    85	
    86	#if _GLIBCXX_INLINE_VERSION
    87	  template<typename _Tp>
    88	    using __aligned_buffer = __aligned_membuf<_Tp>;
    89	#else
    90	  // Similar to __aligned_membuf but aligned for complete objects, not members.
    91	  // This type is used in <forward_list>, <future>, <bits/shared_ptr_base.h>
    92	  // and <bits/hashtable_policy.h>, but ideally they would use __aligned_membuf
    93	  // instead, as it has smaller size for some types on some targets.
    94	  // This type is still used to avoid an ABI change.
    95	  template<typename _Tp>
    96	    struct __aligned_buffer
    97	    {
    98	      // Using __alignof__ gives the alignment for a complete object.
    99	      alignas(__alignof__(_Tp)) unsigned char _M_storage[sizeof(_Tp)];
   100	
   101	      __aligned_buffer() = default;
   102	
   103	      // Can be used to avoid value-initialization
   104	      __aligned_buffer(std::nullptr_t) { }
   105	
   106	      void*
   107	      _M_addr() noexcept
   108	      {
   109	        return static_cast<void*>(&_M_storage);
   110	      }
   111	
   112	      const void*
   113	      _M_addr() const noexcept
   114	      {
   115	        return static_cast<const void*>(&_M_storage);
   116	      }
   117	
   118	      _Tp*
   119	      _M_ptr() noexcept
   120	      { return static_cast<_Tp*>(_M_addr()); }
   121	
   122	      const _Tp*
   123	      _M_ptr() const noexcept
   124	      { return static_cast<const _Tp*>(_M_addr()); }
   125	    };
   126	#endif
   127	
   128	} // namespace
   129	
   130	#endif /* _ALIGNED_BUFFER_H */