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std::bad_variant_access(3)     C++ Standard Libary    std::bad_variant_access(3)

NAME
     std::bad_variant_access - std::bad_variant_access

Synopsis
	Defined in header <variant>
	class bad_variant_access : public std::exception  (since C++17)

	std::bad_variant_access  is the type of the exception thrown in the fol-
     lowing
	situations:

	  * std::get(std::variant) called with an index or type  that  does  not
     match the
	    currently active alternative.
	  * std::visit called to visit a variant that is valueless_by_exception.

Member functions
	constructor   constructs a new bad_variant_access object
		      (public member function)
	operator=     replaces the bad_variant_access object
		      (public member function)
	what	      returns the explanatory string
		      (public member function)

     std::bad_variant_access::bad_variant_access

	bad_variant_access()	noexcept;				     (1)
     (since C++17)
	bad_variant_access( const  bad_variant_access&	other  )  noexcept;  (2)
     (since C++17)

	Constructs  a  new  bad_variant_access object with an implementation-de-
     fined
	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_variant_access then std::strcmp(what(), other.what()) == 0.

Parameters
	other - another exception object to copy

     std::bad_variant_access::operator=

	bad_variant_access&  operator=(  const	 bad_variant_access&   other   )
     (since C++17)
	noexcept;

	Assigns  the  contents with those of other. If *this and other both have
     dynamic type
	std::bad_variant_access then std::strcmp(what(), other.what()) == 0  af-
     ter
	assignment.

Parameters
	other - another exception object to assign with

Return value
	*this

     std::bad_variant_access::what

	virtual const char* what() const noexcept;  (since C++17)

	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 <variant>

      int main()
      {
	  std::variant<int, float> v;
	  v = 12;
	  try
	  {
	      std::get<float>(v);
	  }
	  catch (const std::bad_variant_access& e)
	  {
	      std::cout << e.what() << '\n';
	  }
      }

Possible output:
      bad_variant_access

See also
	get(std::variant)  reads the value of the variant given the index or the
     type (if the
	(C++17) 	  type is unique), throws on error
			  (function template)
	visit		  calls the provided functor with the arguments held  by
     one or more
	(C++17) 	  variants
			  (function template)

http://cppreference.com 	   2024.06.10	      std::bad_variant_access(3)
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