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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../types/bad_typeid.html below:

std::bad_typeid - cppreference.com

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

Inheritance diagram

[edit] Member functions constructs a new bad_typeid object
(public member function) replaces the bad_typeid object
(public member function) 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)
(constexpr since C++26) (2)

bad_typeid( const bad_typeid& other ) throw();

(until C++11)

bad_typeid( const bad_typeid& other ) noexcept;

(since C++11)
(constexpr since C++26)

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)
(constexpr since C++26)

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

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 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 std::exception Member functions destroys the exception object
(virtual public member function of std::exception) [edit] returns an explanatory string
(virtual public member function of std::exception) [edit] [edit] Notes [edit] Example

#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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