Namespaces
Variants
Views
Actions

std::bad_variant_access

From cppreference.com
< cpp‎ | utility‎ | variant
 
 
Utilities library
General utilities
Date and time
Function objects
Formatting library (C++20)
(C++11)
Relational operators (deprecated in C++20)
Integer comparison functions
(C++20)
Swap and type operations
(C++14)
(C++11)
(C++11)
(C++11)
(C++17)
Common vocabulary types
(C++11)
(C++17)
(C++17)
(C++17)
(C++17)

Elementary string conversions
(C++17)
(C++17)
 
 
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 following situations:

Contents

[edit] 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-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_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 ) noexcept;
(since C++17)

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 after 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

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

[edit] Example

#include <variant>
#include <iostream>
 
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

[edit] See also

reads the value of the variant given the index or the type (if the type is unique), throws on error
(function template) [edit]
(C++17)
calls the provided functor with the arguments held by one or more variants
(function template) [edit]