std::bad_typeid

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bad_typeid
Defined in header <typeinfo>
class bad_typeid : public std::exception ;

An exception of this type is thrown when a typeid operator is applied to a dereferenced null pointer value of a polymorphic type.

cpp/error/exception std-bad typeid-inheritance.svg

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

(1)
bad_typeid() throw();
 (until C++11)
bad_typeid() noexcept;
 (since C++11)
(2)
bad_typeid( const bad_typeid& other ) throw ( ) ;
(until C++11)
bad_typeid( const bad_typeid& other ) noexcept;
(since C++11)

Constructs a new bad_typeid object with an implementation-defined null-terminated byte string which is accessible through what().

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= ( const bad_typeid& other ) throw ( ) ;
(until C++11)
bad_typeid& operator= ( const bad_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 (since C++11)

Parameters

other - another exception object to assign with

Return value

*this

std::bad_typeid::what

virtual const char * what( ) const throw ( ) ;
(until C++11)
virtual const char * what( ) const noexcept ;
(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 std::wstring

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 std::exception

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

Feature-test macro Value Std Feature
__cpp_lib_constexpr_exceptions 202411L (C++26) constexpr for exception types

Example

Run this code
#include <iostream>
#include <typeinfo>
 
struct S // The type has to be polymorphic
{
    virtual void f();
}; 
 
int main()
{
    S* p = nullptr;
    try
    {
        std::cout << typeid(*p).name() << '\n';
    }
    catch (const std::bad_typeid& e)
    {
        std::cout << e.what() << '\n';
    }
}

Possible output: 

Attempted a typeid of NULL pointer!
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