typeinfo

Go to the documentation of this file.

// RTTI support for -*- C++ -*-
// Copyright (C) 1994-2026 Free Software Foundation, Inc.
//
// This file is part of GCC.
//
// GCC is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 3, or (at your option)
// any later version.
//
// GCC is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// Under Section 7 of GPL version 3, you are granted additional
// permissions described in the GCC Runtime Library Exception, version
// 3.1, as published by the Free Software Foundation.
 
// You should have received a copy of the GNU General Public License and
// a copy of the GCC Runtime Library Exception along with this program;
// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
// <http://www.gnu.org/licenses/>.
 
/** @file typeinfo
 *  This is a Standard C++ Library header.
 */
 
#ifndef _TYPEINFO
#define _TYPEINFO
 
#ifdef _GLIBCXX_SYSHDR
#pragma GCC system_header
#endif
 
#include <bits/exception.h>
#if __cplusplus >= 201103L
#include <bits/hash_bytes.h>
#endif
 
#define __glibcxx_want_constexpr_typeinfo
#include <bits/version.h>
 
#pragma GCC visibility push(default)
 
extern "C++" {
 
namespace __cxxabiv1
{
  class __class_type_info;
} // namespace __cxxabiv1
 
// Determine whether typeinfo names for the same type are merged (in which
// case comparison can just compare pointers) or not (in which case strings
// must be compared), and whether comparison is to be implemented inline or
// not.  We used to do inline pointer comparison by default if weak symbols
// are available, but even with weak symbols sometimes names are not merged
// when objects are loaded with RTLD_LOCAL, so now we always use strcmp by
// default.  For ABI compatibility, we do the strcmp inline if weak symbols
// are available, and out-of-line if not.  Out-of-line pointer comparison
// is used where the object files are to be portable to multiple systems,
// some of which may not be able to use pointer comparison, but the
// particular system for which libstdc++ is being built can use pointer
// comparison; in particular for most ARM EABI systems, where the ABI
// specifies out-of-line comparison.  The compiler's target configuration
// can override the defaults by defining __GXX_TYPEINFO_EQUALITY_INLINE to
// 1 or 0 to indicate whether or not comparison is inline, and
// __GXX_MERGED_TYPEINFO_NAMES to 1 or 0 to indicate whether or not pointer
// comparison can be used.
 
#ifndef __GXX_MERGED_TYPEINFO_NAMES
// By default, typeinfo names are not merged.
#define __GXX_MERGED_TYPEINFO_NAMES 0
#endif
 
// By default follow the old inline rules to avoid ABI changes.
#ifndef __GXX_TYPEINFO_EQUALITY_INLINE
#  if !__GXX_WEAK__
#    define __GXX_TYPEINFO_EQUALITY_INLINE 0
#  else
#    define __GXX_TYPEINFO_EQUALITY_INLINE 1
#  endif
#endif
 
namespace std
{
  /**
   *  @brief  Part of RTTI.
   *
   *  The @c type_info class describes type information generated by
   *  an implementation.
  */
  class type_info
  {
  public:
    /** Destructor first. Being the first non-inline virtual function, this
     *  controls in which translation unit the vtable is emitted. The
     *  compiler makes use of that information to know where to emit
     *  the runtime-mandated type_info structures in the new-abi.  */
    virtual ~type_info();
 
    /** Returns an @e implementation-defined byte string; this is not
     *  portable between compilers!  */
    const char* name() const _GLIBCXX_NOEXCEPT
    { return __name[0] == '*' ? __name + 1 : __name; }
 
    /** Returns true if `*this` precedes `__arg` in the implementation's
     *  collation order.  */
    bool before(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
 
    _GLIBCXX23_CONSTEXPR
    bool operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT;
 
#if __cpp_impl_three_way_comparison < 201907L
    bool operator!=(const type_info& __arg) const _GLIBCXX_NOEXCEPT
    { return !operator==(__arg); }
#endif
 
#if __cplusplus >= 201103L
    size_t hash_code() const noexcept
    {
#  if !__GXX_MERGED_TYPEINFO_NAMES
      return _Hash_bytes(name(), __builtin_strlen(name()),
                         static_cast<size_t>(0xc70f6907UL));
#  else
      return reinterpret_cast<size_t>(__name);
#  endif
    }
#endif // C++11
 
    // Return true if this is a pointer type of some kind
    virtual bool __is_pointer_p() const;
 
    // Return true if this is a function type
    virtual bool __is_function_p() const;
 
    // Try and catch a thrown type. Store an adjusted pointer to the
    // caught type in THR_OBJ. If THR_TYPE is not a pointer type, then
    // THR_OBJ points to the thrown object. If THR_TYPE is a pointer
    // type, then THR_OBJ is the pointer itself. OUTER indicates the
    // number of outer pointers, and whether they were const
    // qualified.
    virtual bool __do_catch(const type_info *__thr_type, void **__thr_obj,
                            unsigned __outer) const;
 
    // Internally used during catch matching
    virtual bool __do_upcast(const __cxxabiv1::__class_type_info *__target,
                             void **__obj_ptr) const;
 
  protected:
    const char *__name;
 
    explicit type_info(const char *__n): __name(__n) { }
 
  private:
    // type_info objects cannot be copied.
#if __cplusplus >= 201103L
    type_info& operator=(const type_info&) = delete;
    type_info(const type_info&) = delete;
#else
    type_info& operator=(const type_info&);
    type_info(const type_info&);
#endif
 
#if ! __GXX_TYPEINFO_EQUALITY_INLINE
    bool __equal(const type_info&) const _GLIBCXX_NOEXCEPT;
#endif
  };
 
#if __GXX_TYPEINFO_EQUALITY_INLINE
  inline bool
  type_info::before(const type_info& __arg) const _GLIBCXX_NOEXCEPT
  {
#if !__GXX_MERGED_TYPEINFO_NAMES
    // Even with the new abi, on systems that support dlopen
    // we can run into cases where type_info names aren't merged,
    // so we still need to do string comparison.
    if (__name[0] != '*' || __arg.__name[0] != '*')
      return __builtin_strcmp (__name, __arg.__name) < 0;
#else
    // On some targets we can rely on type_info's NTBS being unique,
    // and therefore address comparisons are sufficient.
#endif
 
    // In old abi, or when weak symbols are not supported, there can
    // be multiple instances of a type_info object for one
    // type. Uniqueness must use the __name value, not object address.
    return __name < __arg.__name;
  }
#endif
 
#if __GXX_TYPEINFO_EQUALITY_INLINE || __cplusplus > 202002L
# if ! __GXX_TYPEINFO_EQUALITY_INLINE
  [[__gnu__::__always_inline__]]
# endif
  _GLIBCXX23_CONSTEXPR inline bool
  type_info::operator==(const type_info& __arg) const _GLIBCXX_NOEXCEPT
  {
    if (std::__is_constant_evaluated())
      return this == &__arg;
 
    if (__name == __arg.__name)
      return true;
 
#if !__GXX_TYPEINFO_EQUALITY_INLINE
    // ABI requires comparisons to be non-inline.
    return __equal(__arg);
#elif !__GXX_MERGED_TYPEINFO_NAMES
    // Need to do string comparison.
    return __name[0] != '*' && __builtin_strcmp (__name, __arg.name()) == 0;
#else
    return false;
#endif
  }
#endif
 
 
  /**
   *  @brief  Thrown during incorrect typecasting.
   *  @ingroup exceptions
   *
   *  If you attempt an invalid @c dynamic_cast expression, an instance of
   *  this class (or something derived from this class) is thrown.  */
  class bad_cast : public exception
  {
  public:
    _GLIBCXX26_CONSTEXPR bad_cast() _GLIBCXX_USE_NOEXCEPT { }
 
#if __cplusplus >= 202400L
    [[__gnu__::__gnu_inline__]]
    constexpr inline virtual ~bad_cast() noexcept {}
 
    [[__gnu__::__gnu_inline__]]
    constexpr inline virtual const char* what() const noexcept
    {
      return "std::bad_cast";
    }
#else
    // This declaration is not useless:
    // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
    virtual ~bad_cast() _GLIBCXX_USE_NOEXCEPT;
 
    // See comment in eh_exception.cc.
    virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
#endif
  };
 
  /**
   *  @brief Thrown when a NULL pointer in a @c typeid expression is used.
   *  @ingroup exceptions
   */
  class bad_typeid : public exception
  {
  public:
    _GLIBCXX26_CONSTEXPR bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
 
#if __cplusplus >= 202400L
    [[__gnu__::__gnu_inline__]]
    constexpr inline virtual ~bad_typeid() noexcept {}
 
    [[__gnu__::__gnu_inline__]]
    constexpr inline virtual const char* what() const noexcept
    {
      return "std::bad_typeid";
    }
#else
    // This declaration is not useless:
    // http://gcc.gnu.org/onlinedocs/gcc-3.0.2/gcc_6.html#SEC118
    virtual ~bad_typeid() _GLIBCXX_USE_NOEXCEPT;
 
    // See comment in eh_exception.cc.
    virtual const char* what() const _GLIBCXX_USE_NOEXCEPT;
#endif
  };
} // namespace std
 
} // extern "C++"
 
#pragma GCC visibility pop
 
#endif