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