Difference between revisions of "cpp/utility/variant/bad variant access"
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Andreas Krug (Talk | contribs) m (fmt, ., headers sorted) |
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{{cpp/title|bad_variant_access}} | {{cpp/title|bad_variant_access}} | ||
{{cpp/utility/variant/navbar}} | {{cpp/utility/variant/navbar}} | ||
| − | {{ddcl | since=c++17|header=variant| | + | {{ddcl|since=c++17|header=variant| |
class bad_variant_access : public std::exception | class bad_variant_access : public std::exception | ||
}} | }} | ||
{{tt|std::bad_variant_access}} is the type of the exception thrown in the following situations: | {{tt|std::bad_variant_access}} is the type of the exception thrown in the following situations: | ||
| − | * {{ltt|cpp/utility/variant/get|std::get{{small|(std::variant)}}}} called with an index or type that does not match the currently active alternative | + | * {{ltt|cpp/utility/variant/get|std::get{{small|(std::variant)}}}} called with an index or type that does not match the currently active alternative. |
| − | * {{ltt|cpp/utility/variant/visit|std::visit}} called to visit a variant that is {{ltt|cpp/utility/variant/valueless_by_exception|valueless_by_exception}} | + | * {{ltt|cpp/utility/variant/visit|std::visit}} called to visit a variant that is {{ltt|cpp/utility/variant/valueless_by_exception|valueless_by_exception}}. |
===Member functions=== | ===Member functions=== | ||
| Line 15: | Line 15: | ||
===Example=== | ===Example=== | ||
| − | {{example|code= | + | {{example |
| − | + | |code= | |
#include <iostream> | #include <iostream> | ||
| + | #include <variant> | ||
int main() | int main() | ||
| Line 23: | Line 24: | ||
std::variant<int, float> v; | std::variant<int, float> v; | ||
v = 12; | v = 12; | ||
| − | try { | + | try |
| − | + | { | |
| + | std::get<float>(v); | ||
} | } | ||
| − | catch(const std::bad_variant_access& e) { | + | catch (const std::bad_variant_access& e) |
| + | { | ||
std::cout << e.what() << '\n'; | std::cout << e.what() << '\n'; | ||
} | } | ||
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===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/utility/variant/dsc get}} | + | {{dsc inc|cpp/utility/variant/dsc get}} |
| − | {{dsc inc | cpp/utility/variant/dsc visit}} | + | {{dsc inc|cpp/utility/variant/dsc visit}} |
{{dsc end}} | {{dsc end}} | ||
{{langlinks|es|ja|ru|zh}} | {{langlinks|es|ja|ru|zh}} | ||
Latest revision as of 08:18, 12 October 2023
| 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:
- 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.
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)
|
| [virtual] |
returns an explanatory string (virtual public member function of std::exception)
|
[edit] 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
[edit] See also
| (C++17) |
reads the value of the variant given the index or the type (if the type is unique), throws on error (function template) |
| (C++17) |
calls the provided functor with the arguments held by one or more variants (function template) |
