libstdc++
typeinfo
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1 // RTTI support for -*- C++ -*-
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26 
27 /** @file typeinfo
28  * This is a Standard C++ Library header.
29  */
30 
31 #ifndef _TYPEINFO
32 #define _TYPEINFO
33 
34 #pragma GCC system_header
35 
36 #include <exception>
37 #ifdef __GXX_EXPERIMENTAL_CXX0X__
38 #include <bits/hash_bytes.h>
39 #endif
40 
41 #pragma GCC visibility push(default)
42 
43 extern "C++" {
44 
45 namespace __cxxabiv1
46 {
47  class __class_type_info;
48 } // namespace __cxxabiv1
49 
50 // Determine whether typeinfo names for the same type are merged (in which
51 // case comparison can just compare pointers) or not (in which case strings
52 // must be compared), and whether comparison is to be implemented inline or
53 // not. We used to do inline pointer comparison by default if weak symbols
54 // are available, but even with weak symbols sometimes names are not merged
55 // when objects are loaded with RTLD_LOCAL, so now we always use strcmp by
56 // default. For ABI compatibility, we do the strcmp inline if weak symbols
57 // are available, and out-of-line if not. Out-of-line pointer comparison
58 // is used where the object files are to be portable to multiple systems,
59 // some of which may not be able to use pointer comparison, but the
60 // particular system for which libstdc++ is being built can use pointer
61 // comparison; in particular for most ARM EABI systems, where the ABI
62 // specifies out-of-line comparison. The compiler's target configuration
63 // can override the defaults by defining __GXX_TYPEINFO_EQUALITY_INLINE to
64 // 1 or 0 to indicate whether or not comparison is inline, and
65 // __GXX_MERGED_TYPEINFO_NAMES to 1 or 0 to indicate whether or not pointer
66 // comparison can be used.
67 
68 #ifndef __GXX_MERGED_TYPEINFO_NAMES
69 // By default, typeinfo names are not merged.
70 #define __GXX_MERGED_TYPEINFO_NAMES 0
71 #endif
72 
73 // By default follow the old inline rules to avoid ABI changes.
74 #ifndef __GXX_TYPEINFO_EQUALITY_INLINE
75  #if !__GXX_WEAK__
76  #define __GXX_TYPEINFO_EQUALITY_INLINE 0
77  #else
78  #define __GXX_TYPEINFO_EQUALITY_INLINE 1
79  #endif
80 #endif
81 
82 namespace std
83 {
84  /**
85  * @brief Part of RTTI.
86  *
87  * The @c type_info class describes type information generated by
88  * an implementation.
89  */
90  class type_info
91  {
92  public:
93  /** Destructor first. Being the first non-inline virtual function, this
94  * controls in which translation unit the vtable is emitted. The
95  * compiler makes use of that information to know where to emit
96  * the runtime-mandated type_info structures in the new-abi. */
97  virtual ~type_info();
98 
99  /** Returns an @e implementation-defined byte string; this is not
100  * portable between compilers! */
101  const char* name() const
102  { return __name[0] == '*' ? __name + 1 : __name; }
103 
104 #if !__GXX_TYPEINFO_EQUALITY_INLINE
105  // In old abi, or when weak symbols are not supported, there can
106  // be multiple instances of a type_info object for one
107  // type. Uniqueness must use the _name value, not object address.
108  bool before(const type_info& __arg) const;
109  bool operator==(const type_info& __arg) const;
110 #else
111  #if !__GXX_MERGED_TYPEINFO_NAMES
112  /** Returns true if @c *this precedes @c __arg in the implementation's
113  * collation order. */
114  // Even with the new abi, on systems that support dlopen
115  // we can run into cases where type_info names aren't merged,
116  // so we still need to do string comparison.
117  bool before(const type_info& __arg) const
118  { return (__name[0] == '*' && __arg.__name[0] == '*')
119  ? __name < __arg.__name
120  : __builtin_strcmp (__name, __arg.__name) < 0; }
121 
122  bool operator==(const type_info& __arg) const
123  {
124  return ((__name == __arg.__name)
125  || (__name[0] != '*' &&
126  __builtin_strcmp (__name, __arg.__name) == 0));
127  }
128  #else
129  // On some targets we can rely on type_info's NTBS being unique,
130  // and therefore address comparisons are sufficient.
131  bool before(const type_info& __arg) const
132  { return __name < __arg.__name; }
133 
134  bool operator==(const type_info& __arg) const
135  { return __name == __arg.__name; }
136  #endif
137 #endif
138  bool operator!=(const type_info& __arg) const
139  { return !operator==(__arg); }
140 
141 #ifdef __GXX_EXPERIMENTAL_CXX0X__
142  size_t hash_code() const noexcept
143  {
144 # if !__GXX_MERGED_TYPEINFO_NAMES
145  return _Hash_bytes(name(), __builtin_strlen(name()),
146  static_cast<size_t>(0xc70f6907UL));
147 # else
148  return reinterpret_cast<size_t>(__name);
149 # endif
150  }
151 #endif // __GXX_EXPERIMENTAL_CXX0X__
152 
153  // Return true if this is a pointer type of some kind
154  virtual bool __is_pointer_p() const;
155 
156  // Return true if this is a function type
157  virtual bool __is_function_p() const;
158 
159  // Try and catch a thrown type. Store an adjusted pointer to the
160  // caught type in THR_OBJ. If THR_TYPE is not a pointer type, then
161  // THR_OBJ points to the thrown object. If THR_TYPE is a pointer
162  // type, then THR_OBJ is the pointer itself. OUTER indicates the
163  // number of outer pointers, and whether they were const
164  // qualified.
165  virtual bool __do_catch(const type_info *__thr_type, void **__thr_obj,
166  unsigned __outer) const;
167 
168  // Internally used during catch matching
169  virtual bool __do_upcast(const __cxxabiv1::__class_type_info *__target,
170  void **__obj_ptr) const;
171 
172  protected:
173  const char *__name;
174 
175  explicit type_info(const char *__n): __name(__n) { }
176 
177  private:
178  /// Assigning type_info is not supported.
179  type_info& operator=(const type_info&);
180  type_info(const type_info&);
181  };
182 
183  /**
184  * @brief Thrown during incorrect typecasting.
185  * @ingroup exceptions
186  *
187  * If you attempt an invalid @c dynamic_cast expression, an instance of
188  * this class (or something derived from this class) is thrown. */
189  class bad_cast : public exception
190  {
191  public:
192  bad_cast() _GLIBCXX_USE_NOEXCEPT { }
193 
194  // This declaration is not useless:
195  // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
196  virtual ~bad_cast() _GLIBCXX_USE_NOEXCEPT;
197 
198  // See comment in eh_exception.cc.
199  virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
200  };
201 
202  /**
203  * @brief Thrown when a NULL pointer in a @c typeid expression is used.
204  * @ingroup exceptions
205  */
206  class bad_typeid : public exception
207  {
208  public:
209  bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
210 
211  // This declaration is not useless:
212  // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
213  virtual ~bad_typeid() _GLIBCXX_USE_NOEXCEPT;
214 
215  // See comment in eh_exception.cc.
216  virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
217  };
218 } // namespace std
219 
220 } // extern "C++"
221 
222 #pragma GCC visibility pop
223 
224 #endif