Where Online Learning is simpler!
The C and C++ Include Header Files
cat -n /usr/include/c++/15/bits/stl_construct.h
1 // nonstandard construct and destroy functions -*- C++ -*- 2 3 // Copyright (C) 2001-2025 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 /* 26 * 27 * Copyright (c) 1994 28 * Hewlett-Packard Company 29 * 30 * Permission to use, copy, modify, distribute and sell this software 31 * and its documentation for any purpose is hereby granted without fee, 32 * provided that the above copyright notice appear in all copies and 33 * that both that copyright notice and this permission notice appear 34 * in supporting documentation. Hewlett-Packard Company makes no 35 * representations about the suitability of this software for any 36 * purpose. It is provided "as is" without express or implied warranty. 37 * 38 * 39 * Copyright (c) 1996,1997 40 * Silicon Graphics Computer Systems, Inc. 41 * 42 * Permission to use, copy, modify, distribute and sell this software 43 * and its documentation for any purpose is hereby granted without fee, 44 * provided that the above copyright notice appear in all copies and 45 * that both that copyright notice and this permission notice appear 46 * in supporting documentation. Silicon Graphics makes no 47 * representations about the suitability of this software for any 48 * purpose. It is provided "as is" without express or implied warranty. 49 */ 50 51 /** @file bits/stl_construct.h 52 * This is an internal header file, included by other library headers. 53 * Do not attempt to use it directly. @headername{memory} 54 */ 55 56 #ifndef _STL_CONSTRUCT_H 57 #define _STL_CONSTRUCT_H 1 58 59 #include <new> 60 #include <bits/move.h> 61 #include <bits/stl_iterator_base_types.h> // for iterator_traits 62 #include <bits/stl_iterator_base_funcs.h> // for advance 63 64 /* This file provides the C++17 functions std::destroy_at, std::destroy, and 65 * std::destroy_n, and the C++20 function std::construct_at. 66 * It also provides std::_Construct, std::_Destroy,and std::_Destroy_n functions 67 * which are defined in all standard modes and so can be used in C++98-14 code. 68 * The _Destroy functions will dispatch to destroy_at during constant 69 * evaluation, because calls to that function are intercepted by the compiler 70 * to allow use in constant expressions. 71 */ 72 73 namespace std _GLIBCXX_VISIBILITY(default) 74 { 75 _GLIBCXX_BEGIN_NAMESPACE_VERSION 76 77 #if __glibcxx_raw_memory_algorithms // >= C++17 78 template <typename _Tp> 79 _GLIBCXX20_CONSTEXPR inline void 80 destroy_at(_Tp* __location) 81 { 82 if constexpr (__cplusplus > 201703L && is_array_v<_Tp>) 83 { 84 for (auto& __x : *__location) 85 std::destroy_at(std::__addressof(__x)); 86 } 87 else 88 __location->~_Tp(); 89 } 90 91 #if __cpp_constexpr_dynamic_alloc // >= C++20 92 template<typename _Tp, typename... _Args> 93 requires (!is_unbounded_array_v<_Tp>) 94 && requires { ::new((void*)0) _Tp(std::declval<_Args>()...); } 95 constexpr _Tp* 96 construct_at(_Tp* __location, _Args&&... __args) 97 noexcept(noexcept(::new((void*)0) _Tp(std::declval<_Args>()...))) 98 { 99 void* __loc = __location; 100 // _GLIBCXX_RESOLVE_LIB_DEFECTS 101 // 3436. std::construct_at should support arrays 102 if constexpr (is_array_v<_Tp>) 103 { 104 static_assert(sizeof...(_Args) == 0, "std::construct_at for array " 105 "types must not use any arguments to initialize the " 106 "array"); 107 return ::new(__loc) _Tp[1](); 108 } 109 else 110 return ::new(__loc) _Tp(std::forward<_Args>(__args)...); 111 } 112 #endif // C++20 113 #endif// C++17 114 115 /** 116 * Constructs an object in existing memory by invoking an allocated 117 * object's constructor with an initializer. 118 */ 119 #if __cplusplus >= 201103L 120 template<typename _Tp, typename... _Args> 121 _GLIBCXX20_CONSTEXPR 122 inline void 123 _Construct(_Tp* __p, _Args&&... __args) 124 { 125 #if __cpp_constexpr_dynamic_alloc // >= C++20 126 if (std::__is_constant_evaluated()) 127 { 128 // Allow std::_Construct to be used in constant expressions. 129 std::construct_at(__p, std::forward<_Args>(__args)...); 130 return; 131 } 132 #endif 133 ::new(static_cast<void*>(__p)) _Tp(std::forward<_Args>(__args)...); 134 } 135 #else 136 template<typename _T1, typename _T2> 137 inline void 138 _Construct(_T1* __p, const _T2& __value) 139 { 140 // _GLIBCXX_RESOLVE_LIB_DEFECTS 141 // 402. wrong new expression in [some_]allocator::construct 142 ::new(static_cast<void*>(__p)) _T1(__value); 143 } 144 #endif 145 146 template<typename _T1> 147 _GLIBCXX26_CONSTEXPR 148 inline void 149 _Construct_novalue(_T1* __p) 150 { ::new(static_cast<void*>(__p)) _T1; } 151 152 template<typename _ForwardIterator> 153 _GLIBCXX20_CONSTEXPR void 154 _Destroy(_ForwardIterator __first, _ForwardIterator __last); 155 156 /** 157 * Destroy the object pointed to by a pointer type. 158 */ 159 template<typename _Tp> 160 _GLIBCXX14_CONSTEXPR inline void 161 _Destroy(_Tp* __pointer) 162 { 163 #if __cpp_constexpr_dynamic_alloc // >= C++20 164 std::destroy_at(__pointer); 165 #else 166 __pointer->~_Tp(); 167 #endif 168 } 169 170 #pragma GCC diagnostic push 171 #pragma GCC diagnostic ignored "-Wc++17-extensions" // for if-constexpr 172 173 #if __cplusplus < 201103L 174 template<bool> 175 struct _Destroy_aux 176 { 177 template<typename _ForwardIterator> 178 static _GLIBCXX20_CONSTEXPR void 179 __destroy(_ForwardIterator __first, _ForwardIterator __last) 180 { 181 for (; __first != __last; ++__first) 182 std::_Destroy(std::__addressof(*__first)); 183 } 184 185 template<typename _ForwardIterator, typename _Size> 186 static _GLIBCXX20_CONSTEXPR _ForwardIterator 187 __destroy_n(_ForwardIterator __first, _Size __count) 188 { 189 for (; __count > 0; (void)++__first, --__count) 190 std::_Destroy(std::__addressof(*__first)); 191 return __first; 192 } 193 }; 194 195 template<> 196 struct _Destroy_aux<true> 197 { 198 template<typename _ForwardIterator> 199 static void 200 __destroy(_ForwardIterator, _ForwardIterator) { } 201 202 template<typename _ForwardIterator, typename _Size> 203 static _ForwardIterator 204 __destroy_n(_ForwardIterator __first, _Size __count) 205 { 206 std::advance(__first, __count); 207 return __first; 208 } 209 }; 210 #endif 211 212 /** 213 * Destroy a range of objects. If the value_type of the object has 214 * a trivial destructor, the compiler should optimize all of this 215 * away, otherwise the objects' destructors must be invoked. 216 */ 217 template<typename _ForwardIterator> 218 _GLIBCXX20_CONSTEXPR inline void 219 _Destroy(_ForwardIterator __first, _ForwardIterator __last) 220 { 221 typedef typename iterator_traits<_ForwardIterator>::value_type 222 _Value_type; 223 #if __cplusplus >= 201103L 224 if constexpr (!is_trivially_destructible<_Value_type>::value) 225 for (; __first != __last; ++__first) 226 std::_Destroy(std::__addressof(*__first)); 227 #if __cpp_constexpr_dynamic_alloc // >= C++20 228 else if (std::__is_constant_evaluated()) 229 for (; __first != __last; ++__first) 230 std::destroy_at(std::__addressof(*__first)); 231 #endif 232 #else 233 std::_Destroy_aux<__has_trivial_destructor(_Value_type)>:: 234 __destroy(__first, __last); 235 #endif 236 } 237 238 /** 239 * Destroy a range of objects. If the value_type of the object has 240 * a trivial destructor, the compiler should optimize all of this 241 * away, otherwise the objects' destructors must be invoked. 242 */ 243 template<typename _ForwardIterator, typename _Size> 244 _GLIBCXX20_CONSTEXPR inline _ForwardIterator 245 _Destroy_n(_ForwardIterator __first, _Size __count) 246 { 247 typedef typename iterator_traits<_ForwardIterator>::value_type 248 _Value_type; 249 #if __cplusplus >= 201103L 250 if constexpr (!is_trivially_destructible<_Value_type>::value) 251 for (; __count > 0; (void)++__first, --__count) 252 std::_Destroy(std::__addressof(*__first)); 253 #if __cpp_constexpr_dynamic_alloc // >= C++20 254 else if (std::__is_constant_evaluated()) 255 for (; __count > 0; (void)++__first, --__count) 256 std::destroy_at(std::__addressof(*__first)); 257 #endif 258 else 259 std::advance(__first, __count); 260 return __first; 261 #else 262 return std::_Destroy_aux<__has_trivial_destructor(_Value_type)>:: 263 __destroy_n(__first, __count); 264 #endif 265 } 266 #pragma GCC diagnostic pop 267 268 #if __glibcxx_raw_memory_algorithms // >= C++17 269 template <typename _ForwardIterator> 270 _GLIBCXX20_CONSTEXPR inline void 271 destroy(_ForwardIterator __first, _ForwardIterator __last) 272 { 273 std::_Destroy(__first, __last); 274 } 275 276 template <typename _ForwardIterator, typename _Size> 277 _GLIBCXX20_CONSTEXPR inline _ForwardIterator 278 destroy_n(_ForwardIterator __first, _Size __count) 279 { 280 return std::_Destroy_n(__first, __count); 281 } 282 #endif // C++17 283 284 _GLIBCXX_END_NAMESPACE_VERSION 285 } // namespace std 286 287 #endif /* _STL_CONSTRUCT_H */
