std::get_if (std::variant)

 

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Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros(C++20) Program utilities Variadic functions initializer_list (C++11) is_constant_evaluated (C++20) is_within_lifetime (C++26) source_location (C++20) Coroutine support(C++20) Contract support(C++26) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

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std::variant

Member functions

variant::variant

variant::~variant

variant::operator=

Observers

variant::index

variant::valueless_by_exception

Modifiers

variant::emplace

variant::swap

Visitation

variant::visit (C++26)

Non-member functions

visit(std::variant)

holds_alternative

get(std::variant)

get_if

operator==operator!=operator<operator<=operator>operator>=operator<=> (C++20)

swap(std::variant)

Helper classes

monostate

bad_variant_access

variant_size

variant_alternative

hash<std::variant>

Helper objects

variant_npos

 

Defined in header <variant>
	(1)	(since C++17)
template<std::size_t I, class... Types> constexprstd::add_pointer_t<std::variant_alternative_t<I, std::variant<Types...>>>     get_if(std::variant<Types...>* pv )noexcept;
template<std::size_t I, class... Types> constexprstd::add_pointer_t<conststd::variant_alternative_t<I, std::variant<Types...>>>     get_if(conststd::variant<Types...>* pv )noexcept;
			(2)	(since C++17)
template<class T, class... Types> constexprstd::add_pointer_t<T>     get_if(std::variant<Types...>* pv )noexcept;
template<class T, class... Types> constexprstd::add_pointer_t<const T>     get_if(conststd::variant<Types...>* pv )noexcept;

1) Index-based non-throwing accessor: If pv is not a null pointer and pv->index()== I, returns a pointer to the value stored in the variant pointed to by pv. Otherwise, returns a null pointer value. The call is ill-formed if I is not a valid index in the variant.

2) Type-based non-throwing accessor: Equivalent to (1) with I being the zero-based index of T in Types.... The call is ill-formed if T is not a unique element of Types....

Template parameters

I	-	index to look up
Type	-	unique type to look up

Parameters

pv

-

pointer to a variant

Return value

Pointer to the value stored in the pointed-to variant or null pointer on error.

Example

Run this code

#include <iostream>#include <variant>   int main(){auto check_value =[](conststd::variant<int, float>& v){if(constint* pval = std::get_if<int>(&v))std::cout<<"variant value: "<<*pval <<'\n';elsestd::cout<<"failed to get value!"<<'\n';};   std::variant<int, float> v{12}, w{3.f}; check_value(v); check_value(w);}

Output:

variant value: 12 failed to get value!

See also

get(std::variant) (C++17)

reads the value of the variant given the index or the type (if the type is unique), throws on error (function template)