std::bad_cast - cppreference.com (original) (raw)

An exception of this type is thrown when a dynamic_cast to a reference type fails the run-time check (e.g., because the types are not related by inheritance), and also from std::use_facet if the requested facet does not exist in the locale.

Inheritance diagram

Contents

• 1 Member functions
• 2 std::bad_cast::bad_cast
  • 2.1 Parameters
• 3 std::bad_cast::operator=
  • 3.1 Parameters
  • 3.2 Return value
• 4 std::bad_cast::what
  • 4.1 Return value
  • 4.2 Notes
• 5 Inherited from std::exception
  • 5.1 Member functions
  • 5.2 Notes
  • 5.3 Example

[edit] Member functions

| | constructs a new bad_cast object (public member function) | | ------------------------------------------------------------- | | | replaces the bad_cast object (public member function) | | | returns the explanatory string (public member function) |

std::bad_cast::bad_cast

| (1) | | | | --------------------------------------------- | | ------------------------------------- | | bad_cast() throw(); | | (until C++11) | | bad_cast() noexcept; | | (since C++11) (constexpr since C++26) | | (2) | | | | bad_cast( const bad_cast& other ) throw(); | | (until C++11) | | bad_cast( const bad_cast& other ) noexcept; | | (since C++11) (constexpr since C++26) |

Constructs a new bad_cast 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_cast then std::strcmp(what(), other.what()) == 0.(since C++11)

Parameters

std::bad_cast::operator=

| bad_cast& operator=( const bad_cast& other ) throw(); | | (until C++11) | | --------------------------------------------------------- | | ------------------------------------- | | bad_cast& operator=( const bad_cast& 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_cast then std::strcmp(what(), other.what()) == 0 after assignment.(since C++11)

Parameters

Return value

*this

std::bad_cast::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.

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 #include   struct Foo { virtual Foo() {} }; struct Bar { virtual ~Bar() { std::cout << "Bar\n"; } }; struct Pub : Bar { Pub() override { std::cout << "Pub\n"; } };   int main() { Pub pub; try { [[maybe_unused]] Bar& r1 = dynamic_cast<Bar&>(pub); // OK, upcast   [[maybe_unused]] Foo& r2 = dynamic_cast<Foo&>(pub); // throws } catch (const std::bad_cast& e) { std::cout << "e.what(): " << e.what() << '\n'; } }

Possible output:

e.what(): std::bad_cast ~Pub ~Bar