libstdc++: typeinfo Source File

libstdc++

typeinfo
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1// RTTI support for -*- C++ -*-
2// Copyright (C) 1994-2026 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
46extern "C++" {
47
48namespace __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
85namespace 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 _GLIBCXX26_CONSTEXPR bad_cast() _GLIBCXX_USE_NOEXCEPT { }
228
229#if __cplusplus >= 202400L
230 [[__gnu__::__gnu_inline__]]
231 constexpr inline virtual ~bad_cast() noexcept {}
232
233 [[__gnu__::__gnu_inline__]]
234 constexpr inline virtual const char* what() const noexcept
235 {
236 return "std::bad_cast";
237 }
238#else
239 // This declaration is not useless:
240 // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
241 virtual ~bad_cast() _GLIBCXX_USE_NOEXCEPT;
242
243 // See comment in eh_exception.cc.
244 virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
245#endif
246 };
247
248 /**
249 * @brief Thrown when a NULL pointer in a @c typeid expression is used.
250 * @ingroup exceptions
251 */
252 class bad_typeid : public exception
253 {
254 public:
255 _GLIBCXX26_CONSTEXPR bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
256
257#if __cplusplus >= 202400L
258 [[__gnu__::__gnu_inline__]]
259 constexpr inline virtual ~bad_typeid() noexcept {}
260
261 [[__gnu__::__gnu_inline__]]
262 constexpr inline virtual const char* what() const noexcept
263 {
264 return "std::bad_typeid";
265 }
266#else
267 // This declaration is not useless:
268 // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
269 virtual ~bad_typeid() _GLIBCXX_USE_NOEXCEPT;
270
271 // See comment in eh_exception.cc.
272 virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
273#endif
274 };
275} // namespace std
276
277} // extern "C++"
278
279#pragma GCC visibility pop
280
281#endif
version.h
exception.h
hash_bytes.h
std
ISO C++ entities toplevel namespace is std.
std::type_info
Part of RTTI.
Definition typeinfo:94
std::type_info::name
const char * name() const noexcept
Definition typeinfo:104
std::type_info::~type_info
virtual ~type_info()
std::type_info::before
bool before(const type_info &__arg) const noexcept
std::bad_cast
Thrown during incorrect typecasting.
Definition typeinfo:225
std::bad_cast::what
virtual constexpr const char * what() const noexcept
Definition typeinfo:234
std::bad_typeid
Thrown when a NULL pointer in a typeid expression is used.
Definition typeinfo:253
std::bad_typeid::what
virtual constexpr const char * what() const noexcept
Definition typeinfo:262