Where Online Learning is simpler!
The C and C++ Include Header Files
cat -n /usr/include/c++/15/typeinfo
1 // RTTI support for -*- C++ -*- 2 // Copyright (C) 1994-2025 Free Software Foundation, Inc. 3 // 4 // This file is part of GCC. 5 // 6 // GCC is free software; you can redistribute it and/or modify 7 // it under the terms of the GNU General Public License as published by 8 // the Free Software Foundation; either version 3, or (at your option) 9 // any later version. 10 // 11 // GCC 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 typeinfo 26 * This is a Standard C++ Library header. 27 */ 28 29 #ifndef _TYPEINFO 30 #define _TYPEINFO 31 32 #ifdef _GLIBCXX_SYSHDR 33 #pragma GCC system_header 34 #endif 35 36 #include <bits/exception.h> 37 #if __cplusplus >= 201103L 38 #include <bits/hash_bytes.h> 39 #endif 40 41 #define __glibcxx_want_constexpr_typeinfo 42 #include <bits/version.h> 43 44 #pragma GCC visibility push(default) 45 46 extern "C++" { 47 48 namespace __cxxabiv1 49 { 50 class __class_type_info; 51 } // namespace __cxxabiv1 52 53 // Determine whether typeinfo names for the same type are merged (in which 54 // case comparison can just compare pointers) or not (in which case strings 55 // must be compared), and whether comparison is to be implemented inline or 56 // not. We used to do inline pointer comparison by default if weak symbols 57 // are available, but even with weak symbols sometimes names are not merged 58 // when objects are loaded with RTLD_LOCAL, so now we always use strcmp by 59 // default. For ABI compatibility, we do the strcmp inline if weak symbols 60 // are available, and out-of-line if not. Out-of-line pointer comparison 61 // is used where the object files are to be portable to multiple systems, 62 // some of which may not be able to use pointer comparison, but the 63 // particular system for which libstdc++ is being built can use pointer 64 // comparison; in particular for most ARM EABI systems, where the ABI 65 // specifies out-of-line comparison. The compiler's target configuration 66 // can override the defaults by defining __GXX_TYPEINFO_EQUALITY_INLINE to 67 // 1 or 0 to indicate whether or not comparison is inline, and 68 // __GXX_MERGED_TYPEINFO_NAMES to 1 or 0 to indicate whether or not pointer 69 // comparison can be used. 70 71 #ifndef __GXX_MERGED_TYPEINFO_NAMES 72 // By default, typeinfo names are not merged. 73 #define __GXX_MERGED_TYPEINFO_NAMES 0 74 #endif 75 76 // By default follow the old inline rules to avoid ABI changes. 77 #ifndef __GXX_TYPEINFO_EQUALITY_INLINE 78 # if !__GXX_WEAK__ 79 # define __GXX_TYPEINFO_EQUALITY_INLINE 0 80 # else 81 # define __GXX_TYPEINFO_EQUALITY_INLINE 1 82 # endif 83 #endif 84 85 namespace std 86 { 87 /** 88 * @brief Part of RTTI. 89 * 90 * The @c type_info class describes type information generated by 91 * an implementation. 92 */ 93 class type_info 94 { 95 public: 96 /** Destructor first. Being the first non-inline virtual function, this 97 * controls in which translation unit the vtable is emitted. The 98 * compiler makes use of that information to know where to emit 99 * the runtime-mandated type_info structures in the new-abi. */ 100 virtual ~type_info(); 101 102 /** Returns an @e implementation-defined byte string; this is not 103 * portable between compilers! */ 104 const char* name() const _GLIBCXX_NOEXCEPT 105 { return __name[0] == '*' ? __name + 1 : __name; } 106 107 /** Returns true if `*this` precedes `__arg` in the implementation's 108 * collation order. */ 109 bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT; 110 111 _GLIBCXX23_CONSTEXPR 112 bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT; 113 114 #if __cpp_impl_three_way_comparison < 201907L 115 bool operator!=(const type_info& __arg) const _GLIBCXX_NOEXCEPT 116 { return !operator==(__arg); } 117 #endif 118 119 #if __cplusplus >= 201103L 120 size_t hash_code() const noexcept 121 { 122 # if !__GXX_MERGED_TYPEINFO_NAMES 123 return _Hash_bytes(name(), __builtin_strlen(name()), 124 static_cast<size_t>(0xc70f6907UL)); 125 # else 126 return reinterpret_cast<size_t>(__name); 127 # endif 128 } 129 #endif // C++11 130 131 // Return true if this is a pointer type of some kind 132 virtual bool __is_pointer_p() const; 133 134 // Return true if this is a function type 135 virtual bool __is_function_p() const; 136 137 // Try and catch a thrown type. Store an adjusted pointer to the 138 // caught type in THR_OBJ. If THR_TYPE is not a pointer type, then 139 // THR_OBJ points to the thrown object. If THR_TYPE is a pointer 140 // type, then THR_OBJ is the pointer itself. OUTER indicates the 141 // number of outer pointers, and whether they were const 142 // qualified. 143 virtual bool __do_catch(const type_info *__thr_type, void **__thr_obj, 144 unsigned __outer) const; 145 146 // Internally used during catch matching 147 virtual bool __do_upcast(const __cxxabiv1::__class_type_info *__target, 148 void **__obj_ptr) const; 149 150 protected: 151 const char *__name; 152 153 explicit type_info(const char *__n): __name(__n) { } 154 155 private: 156 // type_info objects cannot be copied. 157 #if __cplusplus >= 201103L 158 type_info& operator=(const type_info&) = delete; 159 type_info(const type_info&) = delete; 160 #else 161 type_info& operator=(const type_info&); 162 type_info(const type_info&); 163 #endif 164 165 #if ! __GXX_TYPEINFO_EQUALITY_INLINE 166 bool __equal(const type_info&) const _GLIBCXX_NOEXCEPT; 167 #endif 168 }; 169 170 #if __GXX_TYPEINFO_EQUALITY_INLINE 171 inline bool 172 type_info::before(const type_info& __arg) const _GLIBCXX_NOEXCEPT 173 { 174 #if !__GXX_MERGED_TYPEINFO_NAMES 175 // Even with the new abi, on systems that support dlopen 176 // we can run into cases where type_info names aren't merged, 177 // so we still need to do string comparison. 178 if (__name[0] != '*' || __arg.__name[0] != '*') 179 return __builtin_strcmp (__name, __arg.__name) < 0; 180 #else 181 // On some targets we can rely on type_info's NTBS being unique, 182 // and therefore address comparisons are sufficient. 183 #endif 184 185 // In old abi, or when weak symbols are not supported, there can 186 // be multiple instances of a type_info object for one 187 // type. Uniqueness must use the __name value, not object address. 188 return __name < __arg.__name; 189 } 190 #endif 191 192 #if __GXX_TYPEINFO_EQUALITY_INLINE || __cplusplus > 202002L 193 # if ! __GXX_TYPEINFO_EQUALITY_INLINE 194 [[__gnu__::__always_inline__]] 195 # endif 196 _GLIBCXX23_CONSTEXPR inline bool 197 type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT 198 { 199 if (std::__is_constant_evaluated()) 200 return this == &__arg; 201 202 if (__name == __arg.__name) 203 return true; 204 205 #if !__GXX_TYPEINFO_EQUALITY_INLINE 206 // ABI requires comparisons to be non-inline. 207 return __equal(__arg); 208 #elif !__GXX_MERGED_TYPEINFO_NAMES 209 // Need to do string comparison. 210 return __name[0] != '*' && __builtin_strcmp (__name, __arg.name()) == 0; 211 #else 212 return false; 213 #endif 214 } 215 #endif 216 217 218 /** 219 * @brief Thrown during incorrect typecasting. 220 * @ingroup exceptions 221 * 222 * If you attempt an invalid @c dynamic_cast expression, an instance of 223 * this class (or something derived from this class) is thrown. */ 224 class bad_cast : public exception 225 { 226 public: 227 bad_cast() _GLIBCXX_USE_NOEXCEPT { } 228 229 // This declaration is not useless: 230 // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118 231 virtual ~bad_cast() _GLIBCXX_USE_NOEXCEPT; 232 233 // See comment in eh_exception.cc. 234 virtual const char* what() const _GLIBCXX_USE_NOEXCEPT; 235 }; 236 237 /** 238 * @brief Thrown when a NULL pointer in a @c typeid expression is used. 239 * @ingroup exceptions 240 */ 241 class bad_typeid : public exception 242 { 243 public: 244 bad_typeid () _GLIBCXX_USE_NOEXCEPT { } 245 246 // This declaration is not useless: 247 // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118 248 virtual ~bad_typeid() _GLIBCXX_USE_NOEXCEPT; 249 250 // See comment in eh_exception.cc. 251 virtual const char* what() const _GLIBCXX_USE_NOEXCEPT; 252 }; 253 } // namespace std 254 255 } // extern "C++" 256 257 #pragma GCC visibility pop 258 259 #endif
