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      std::bad_typeid

      From cppreference.com
      <cpp‎ |types
       
       
      Utilities library
       
       
      Defined in header<typeinfo>
      class bad_typeid:publicstd::exception

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

      std-bad typeid-inheritance.svg

      Contents

      [edit]Member functions

      (constructor)
      		 constructs a newbad_typeid object
      (public member function)
      operator=
      		 replaces thebad_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)
      (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 newbad_typeid object with an implementation-defined null-terminated byte string which is accessible throughwhat().

      1) Default constructor.
      2) Copy constructor.If*this andother both have dynamic typestd::bad_typeid thenstd::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 ofother.If*this andother both have dynamic typestd::bad_typeid thenstd::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

      virtualconstchar* what()constthrow();
      		(until C++11)
      virtualconstchar* what()constnoexcept;
      		(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 astd::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 overridewhat().

      Inherited fromstd::exception

      Member functions

      [virtual]
      		 destroys the exception object
      (virtual public member function ofstd::exception)[edit]
      [virtual]
      		 returns an explanatory string
      (virtual public member function ofstd::exception)[edit]

      [edit]Notes

      Feature-test macroValueStdFeature
      __cpp_lib_constexpr_exceptions202411L(C++26)constexpr for exception types

      [edit]Example

      Run this code
      #include <iostream>#include <typeinfo> struct S// The type has to be polymorphic{virtualvoid 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!
      Retrieved from "https://en.cppreference.com/mwiki/index.php?title=cpp/types/bad_typeid&oldid=182975"
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