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std::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/exceptionstd-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 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)

Returns the explanatory string.

Parameters

(none).

Return value

Pointer to a 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.

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)

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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