From cppreference.com
classbad_typeid:publicstd::exception;An exception of this type is thrown when a
operator is applied to a dereferenced null pointer value of a polymorphic type.
Inheritance diagram
Member functions
(constructor)
constructs a new bad_typeid object
(public member function)operator=
replaces the bad_typeid object
(public member function)what
returns the explanatory string
(public member function)std::bad_typeid::bad_typeid
bad_typeid()throw(); (1)(until C++11)bad_typeid()noexcept;(since C++11)bad_typeid(constbad_typeid&other)throw(); (2)(until C++11)bad_typeid(constbad_typeid&other)noexcept;(since C++11)Constructs a new bad_typeid object with an implementation-defined null-terminated byte string which is accessible through
.
1) Default constructor.
2) Copy constructor. If *this and other both have dynamic type std::bad_typeid then std::strcmp(what(),other.what())==0.(since C++11)
Parameters
other - another exception object to copy std::bad_typeid::operator=
bad_typeid&operator=(constbad_typeid&other)throw();(until C++11)bad_typeid&operator=(constbad_typeid&other)noexcept;(since C++11)Assigns the contents with those of other. If *this and other both have dynamic type std::bad_typeid then std::strcmp(what(),other.what())==0 after assignment.(since C++11)
Parameters
other - another exception object to assign with Return value
*this
std::bad_typeid::what
virtualconstchar*what()constthrow();(until C++11)virtualconstchar*what()constnoexcept;(since C++11)
(constexpr since C++26)Returns the explanatory string.
Return value
Pointer to an implementation-defined null-terminated string with explanatory information. The string is suitable for conversion and display as a
. The pointer is guaranteed to be valid at least until the exception object from which it is obtained is destroyed, or until a non-const member function (e.g. copy assignment operator) on the exception object is called.
The returned string is encoded with the ordinary literal encoding during constant evaluation.
(since C++26)Notes
Implementations are allowed but not required to override what().
Inherited from
Member functions
[virtual]
destroys the exception object
(virtual public member function of std::exception)
[virtual]
returns an explanatory string
(virtual public member function of std::exception)
Notes
macroValueStdFeature
__cpp_lib_constexpr_exceptions
(C++26)constexpr for exception types Example
Run this code
#include<iostream>#include<typeinfo>structS// The type has to be polymorphic{virtualvoidf();};intmain(){S*p=nullptr;try{std::cout<<typeid(*p).name()<<'\n';}catch(conststd::bad_typeid&e){std::cout<<e.what()<<'\n';}}Possible output:
Attempted a typeid of NULL pointer!