typeinfo
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// RTTI support for -*- C++ -*-
// Copyright (C) 1994-2022 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
#pragma GCC system_header
#include <bits/exception.h>
#if __cplusplus >= 201103L
#include <bits/hash_bytes.h>
#endif
#pragma GCC visibility push(default)
#if __cplusplus >= 202100L
# define __cpp_lib_constexpr_typeinfo 202106L
#endif
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
_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:
bad_cast() _GLIBCXX_USE_NOEXCEPT { }
// 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;
};
/**
* @brief Thrown when a NULL pointer in a @c typeid expression is used.
* @ingroup exceptions
*/
class bad_typeid : public exception
{
public:
bad_typeid () _GLIBCXX_USE_NOEXCEPT { }
// 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;
};
} // namespace std
} // extern "C++"
#pragma GCC visibility pop
#endif
exception.h
hash_bytes.h
std
ISO C++ entities toplevel namespace is std.
std::type_info
Part of RTTI.
Definition typeinfo:93
std::type_info::name
const char * name() const noexcept
Definition typeinfo:103
std::type_info::~type_info
virtual ~type_info()
std::type_info::before
bool before(const type_info &__arg) const noexcept
std::bad_cast::what
virtual const char * what() const noexcept
std::bad_typeid::what
virtual const char * what() const noexcept