NAME¶

std::bad_typeid - std::bad_typeid

Synopsis¶

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.

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

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

destructor destroys the exception object
[virtual] (virtual public member function of std::exception)
what returns an explanatory string
[virtual] (virtual public member function of std::exception)

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!