libstdc++
typeinfo
Go to the documentation of this file.
1 // RTTI support for -*- C++ -*-
2 // Copyright (C) 1994-2024 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 #pragma GCC system_header
33 
34 #include <bits/exception.h>
35 #if __cplusplus >= 201103L
36 #include <bits/hash_bytes.h>
37 #endif
38 
39 #define __glibcxx_want_constexpr_typeinfo
40 #include <bits/version.h>
41 
42 #pragma GCC visibility push(default)
43 
44 extern "C++" {
45 
46 namespace __cxxabiv1
47 {
48  class __class_type_info;
49 } // namespace __cxxabiv1
50 
51 // Determine whether typeinfo names for the same type are merged (in which
52 // case comparison can just compare pointers) or not (in which case strings
53 // must be compared), and whether comparison is to be implemented inline or
54 // not. We used to do inline pointer comparison by default if weak symbols
55 // are available, but even with weak symbols sometimes names are not merged
56 // when objects are loaded with RTLD_LOCAL, so now we always use strcmp by
57 // default. For ABI compatibility, we do the strcmp inline if weak symbols
58 // are available, and out-of-line if not. Out-of-line pointer comparison
59 // is used where the object files are to be portable to multiple systems,
60 // some of which may not be able to use pointer comparison, but the
61 // particular system for which libstdc++ is being built can use pointer
62 // comparison; in particular for most ARM EABI systems, where the ABI
63 // specifies out-of-line comparison. The compiler's target configuration
64 // can override the defaults by defining __GXX_TYPEINFO_EQUALITY_INLINE to
65 // 1 or 0 to indicate whether or not comparison is inline, and
66 // __GXX_MERGED_TYPEINFO_NAMES to 1 or 0 to indicate whether or not pointer
67 // comparison can be used.
68 
69 #ifndef __GXX_MERGED_TYPEINFO_NAMES
70 // By default, typeinfo names are not merged.
71 #define __GXX_MERGED_TYPEINFO_NAMES 0
72 #endif
73 
74 // By default follow the old inline rules to avoid ABI changes.
75 #ifndef __GXX_TYPEINFO_EQUALITY_INLINE
76 # if !__GXX_WEAK__
77 # define __GXX_TYPEINFO_EQUALITY_INLINE 0
78 # else
79 # define __GXX_TYPEINFO_EQUALITY_INLINE 1
80 # endif
81 #endif
82 
83 namespace std
84 {
85  /**
86  * @brief Part of RTTI.
87  *
88  * The @c type_info class describes type information generated by
89  * an implementation.
90  */
91  class type_info
92  {
93  public:
94  /** Destructor first. Being the first non-inline virtual function, this
95  * controls in which translation unit the vtable is emitted. The
96  * compiler makes use of that information to know where to emit
97  * the runtime-mandated type_info structures in the new-abi. */
98  virtual ~type_info();
99 
100  /** Returns an @e implementation-defined byte string; this is not
101  * portable between compilers! */
102  const char* name() const _GLIBCXX_NOEXCEPT
103  { return __name[0] == '*' ? __name + 1 : __name; }
104 
105  /** Returns true if `*this` precedes `__arg` in the implementation's
106  * collation order. */
107  bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
108 
109  _GLIBCXX23_CONSTEXPR
110  bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
111 
112 #if __cpp_impl_three_way_comparison < 201907L
113  bool operator!=(const type_info& __arg) const _GLIBCXX_NOEXCEPT
114  { return !operator==(__arg); }
115 #endif
116 
117 #if __cplusplus >= 201103L
118  size_t hash_code() const noexcept
119  {
120 # if !__GXX_MERGED_TYPEINFO_NAMES
121  return _Hash_bytes(name(), __builtin_strlen(name()),
122  static_cast<size_t>(0xc70f6907UL));
123 # else
124  return reinterpret_cast<size_t>(__name);
125 # endif
126  }
127 #endif // C++11
128 
129  // Return true if this is a pointer type of some kind
130  virtual bool __is_pointer_p() const;
131 
132  // Return true if this is a function type
133  virtual bool __is_function_p() const;
134 
135  // Try and catch a thrown type. Store an adjusted pointer to the
136  // caught type in THR_OBJ. If THR_TYPE is not a pointer type, then
137  // THR_OBJ points to the thrown object. If THR_TYPE is a pointer
138  // type, then THR_OBJ is the pointer itself. OUTER indicates the
139  // number of outer pointers, and whether they were const
140  // qualified.
141  virtual bool __do_catch(const type_info *__thr_type, void **__thr_obj,
142  unsigned __outer) const;
143 
144  // Internally used during catch matching
145  virtual bool __do_upcast(const __cxxabiv1::__class_type_info *__target,
146  void **__obj_ptr) const;
147 
148  protected:
149  const char *__name;
150 
151  explicit type_info(const char *__n): __name(__n) { }
152 
153  private:
154  // type_info objects cannot be copied.
155 #if __cplusplus >= 201103L
156  type_info& operator=(const type_info&) = delete;
157  type_info(const type_info&) = delete;
158 #else
159  type_info& operator=(const type_info&);
160  type_info(const type_info&);
161 #endif
162 
163 #if ! __GXX_TYPEINFO_EQUALITY_INLINE
164  bool __equal(const type_info&) const _GLIBCXX_NOEXCEPT;
165 #endif
166  };
167 
168 #if __GXX_TYPEINFO_EQUALITY_INLINE
169  inline bool
170  type_info::before(const type_info& __arg) const _GLIBCXX_NOEXCEPT
171  {
172 #if !__GXX_MERGED_TYPEINFO_NAMES
173  // Even with the new abi, on systems that support dlopen
174  // we can run into cases where type_info names aren't merged,
175  // so we still need to do string comparison.
176  if (__name[0] != '*' || __arg.__name[0] != '*')
177  return __builtin_strcmp (__name, __arg.__name) < 0;
178 #else
179  // On some targets we can rely on type_info's NTBS being unique,
180  // and therefore address comparisons are sufficient.
181 #endif
182 
183  // In old abi, or when weak symbols are not supported, there can
184  // be multiple instances of a type_info object for one
185  // type. Uniqueness must use the __name value, not object address.
186  return __name < __arg.__name;
187  }
188 #endif
189 
190 #if __GXX_TYPEINFO_EQUALITY_INLINE || __cplusplus > 202002L
191  _GLIBCXX23_CONSTEXPR inline bool
192  type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
193  {
194  if (std::__is_constant_evaluated())
195  return this == &__arg;
196 
197  if (__name == __arg.__name)
198  return true;
199 
200 #if !__GXX_TYPEINFO_EQUALITY_INLINE
201  // ABI requires comparisons to be non-inline.
202  return __equal(__arg);
203 #elif !__GXX_MERGED_TYPEINFO_NAMES
204  // Need to do string comparison.
205  return __name[0] != '*' && __builtin_strcmp (__name, __arg.name()) == 0;
206 #else
207  return false;
208 #endif
209  }
210 # endif
211 
212 
213  /**
214  * @brief Thrown during incorrect typecasting.
215  * @ingroup exceptions
216  *
217  * If you attempt an invalid @c dynamic_cast expression, an instance of
218  * this class (or something derived from this class) is thrown. */
219  class bad_cast : public exception
220  {
221  public:
222  bad_cast() _GLIBCXX_USE_NOEXCEPT { }
223 
224  // This declaration is not useless:
225  // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
226  virtual ~bad_cast() _GLIBCXX_USE_NOEXCEPT;
227 
228  // See comment in eh_exception.cc.
229  virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
230  };
231 
232  /**
233  * @brief Thrown when a NULL pointer in a @c typeid expression is used.
234  * @ingroup exceptions
235  */
236  class bad_typeid : public exception
237  {
238  public:
239  bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
240 
241  // This declaration is not useless:
242  // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
243  virtual ~bad_typeid() _GLIBCXX_USE_NOEXCEPT;
244 
245  // See comment in eh_exception.cc.
246  virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
247  };
248 } // namespace std
249 
250 } // extern "C++"
251 
252 #pragma GCC visibility pop
253 
254 #endif